Iran's Strait of Hormuz Closure Under International Law

Introduction

The Strait of Hormuz Closure is a legal problem before it is a strategic one. The Strait of Hormuz is not merely a sensitive shipping route. It is a strait used for international navigation, and that legal character places it within a specialized body of rules governing passage, coastal-State powers, and the protection of international maritime traffic (UNCLOS 1982, arts 37–44; Corfu Channel 1949).

The central issue is not simply whether Iran can regulate activity near its coast. Coastal States do have rights in their territorial sea, but those rights are more limited in an international strait than in ordinary coastal waters. The legal question is therefore sharper: can Iran lawfully close, suspend, or materially obstruct passage through a strait that serves as a corridor for global navigation? (UNCLOS 1982, arts 38, 42 and 44)

That question becomes more difficult because Iran is not a party to the 1982 United Nations Convention on the Law of the Sea. A serious legal analysis cannot assume that treaty law automatically binds Iran in the same way it binds States parties. It must examine, separately, Iran’s treaty position, its 1982 declaration, and the extent to which rules on passage through international straits also exist as customary international law (United Nations, Treaty Status; Iran Declaration 1982).

The dispute also cannot be reduced to a single branch of law. Any assessment of a Strait of Hormuz Closure must consider the law of the sea, the prohibition on the use of force, self-defense under Article 51 of the UN Charter, and the rules governing military operations at sea. These bodies of law overlap, but they do not say the same thing, and weak commentary often fails because it merges them without distinction (UN Charter 1945, art 51; Nicaragua 1986; Oil Platforms 2003).

A further complication is that modern interference with navigation does not always take the form of an express declaration of closure. A State may instead impose selective conditions, deny passage to certain vessels, require prior coordination, or create risks that make normal transit practically impossible. International law must therefore address not only formal closure, but also conduct that hampers, impairs, or effectively suspends passage in practice (UNCLOS 1982, art 44).

This article argues that the legality of a Strait of Hormuz Closure turns on three connected questions. First, what navigational regime governs Hormuz as an international strait? Second, whether the relevant rule binds Iran as treaty law, customary law, or both. Third, whether any reliance on self-defense or naval warfare can lawfully justify broad interference with neutral and commercial shipping. The answer to those questions is essential for determining whether Iranian conduct amounts to a lawful maritime regulation or an internationally wrongful restriction on passage.

1. The Strait of Hormuz as a Legal Space

1.1 The geography of the strait

The Strait of Hormuz matters legally because its physical configuration places it within the law of international straits. It connects the Persian Gulf with the Gulf of Oman and the Arabian Sea, and it is used continuously for international navigation by merchant shipping and naval vessels. At its narrowest point, it is about 21 nautical miles wide (39 km), and the navigable inbound and outbound channels are only about 2 miles wide each, separated by a buffer zone (IEA, 2026).

That geography has a direct legal consequence. Iran lies on the northern side of the strait and Oman on the southern side. Both claim a 12-nautical-mile territorial sea. Iran’s 1993 Marine Areas Act expressly extends Iranian sovereignty to its territorial sea in the Strait of Hormuz and fixes the breadth of that sea at 12 nautical miles; it also provides that, where territorial seas overlap, the dividing line is the median line unless otherwise agreed (Iran, 1993).

As a result, the navigable corridor cannot be treated as if it were a normal coastal margin controlled by one State alone. Passage through Hormuz takes place in a narrow maritime space where coastal-State sovereignty exists, but is legally conditioned by the special rules applicable to straits used for international navigation. That is why the legality of any attempted closure must be examined under the law of straits rather than under a simple sovereignty-based argument (UNCLOS, 1982, arts 34 and 37).

1.2 Why ordinary territorial-sea logic is insufficient

Ordinary territorial-sea logic starts from a broad proposition: the coastal State is sovereign in its territorial sea, subject to recognized navigational rights of other States. In an international strait, that starting point is incomplete. UNCLOS makes clear that the sovereignty of States bordering straits is exercised subject to the special regime established for straits used for international navigation and to other rules of international law (UNCLOS, 1982, art. 34).

Hormuz, therefore, cannot be analyzed as if Iran were merely regulating foreign movement along its own shore. The relevant legal question is not simply how far Iranian sovereignty extends, but how that sovereignty operates in a maritime corridor connecting one part of the high seas or exclusive economic zone to another. Under Part III of UNCLOS, that type of strait triggers a distinct regime of passage, and that regime is designed precisely to prevent the bordering State from reducing international navigation to a matter of unilateral permission (UNCLOS, 1982, arts 37–38).

This distinction is essential because much of the later legal debate turns on the difference between innocent passage and transit passage. If Hormuz were treated only through ordinary territorial-sea categories, the analysis would overstate coastal discretion and understate the international character of the route. The law of straits exists because certain maritime spaces serve not only the adjacent State, but the wider international community. Hormuz is one of those spaces.

2. The Law of Passage Through International Straits

2.1 Transit passage under Part III of UNCLOS

The doctrinal starting point is Part III of the United Nations Convention on the Law of the Sea. Article 37 applies that regime to straits used for international navigation between one part of the high seas or exclusive economic zone and another. Hormuz falls naturally within that description because it connects the Persian Gulf to the Gulf of Oman and the wider oceanic system, and because it is used continuously by international shipping and aircraft (UNCLOS, 1982, art. 37).

Article 38 then grants all ships and aircraft the right of transit passage. That right is narrower than full freedom of navigation because it must be exercised continuously and expeditiously. Yet it is also stronger than ordinary innocent passage because it is designed for international corridors whose function would be destroyed if the bordering State could interrupt them at will (UNCLOS, 1982, art. 38).

The core legal rule appears in Article 44. States bordering a strait shall not hamper transit passage, and there shall be no suspension of transit passage. That provision is the central test for any alleged Strait of Hormuz closure. Once the strait is characterized as one governed by transit passage, the legality of closure is examined first against the rules of non-impediment and non-suspension, not against broad and undefined claims of security or political necessity (UNCLOS, 1982, art. 44).

That structure matters because it limits the role of coastal discretion. The legal premise of Part III is that certain narrow waterways perform an international function that cannot be subordinated to unilateral control. A bordering State does not lose sovereignty in its territorial sea, but that sovereignty is exercised within a special legal regime that protects the continuity of passage (Churchill, Lowe and Sander, 2022; Rothwell and Stephens, 2016).

The practical implication is clear. A formal declaration of closure would be the most obvious violation, but it is not the only possible one. Conduct that materially obstructs transit, makes passage contingent on discretionary approval, or renders movement through the strait legally or practically unavailable may also fall within the prohibition on hampering transit passage. The law is directed not only at legal labels, but at real effects on navigation (UNCLOS, 1982, arts 38 and 44).

2.2 The limited regulatory powers of the Straits States

Part III does not leave bordering States without regulatory authority. Articles 41 and 42 allow them to participate in the designation of sea lanes and traffic separation schemes and to adopt laws relating to navigational safety, pollution control, fishing, and customs, fiscal, immigration, or sanitary matters (UNCLOS, 1982, arts 41–42).

Those powers, however, are narrow in purpose and limited in legal effect. Article 42 makes clear that such laws must not discriminate in form or in fact among foreign ships. More importantly, they must not have the practical effect of denying, hampering, or impairing the right of transit passage. The treaty, therefore, draws a firm line between regulation of passage and control over passage (UNCLOS, 1982, art. 42).

That distinction is essential for Hormuz. A coastal State may invoke the language of safety, coordination, or security. Yet legal form does not decide the issue. A measure described as “coordination” may still be unlawful if it gives the coastal State discretionary authority to determine who may pass, on what conditions, and at what time. Once regulation becomes a permission system, it ceases to be ordinary regulation and begins to resemble obstruction (Beckman, 2007; Rothwell and Stephens, 2016).

The same point applies to selective restrictions. A bordering State cannot lawfully transform a general right of transit passage into a privilege enjoyed only by vessels it considers acceptable. The prohibition on hampering passage is incompatible with a regime in which the coastal State sorts foreign shipping into favored and disfavored categories and then conditions transit accordingly. The law of straits is designed to prevent exactly that kind of unilateral leverage over an international corridor (UNCLOS, 1982, arts 42 and 44).

This is why broad appeals to maritime security must be handled carefully. Security concerns are not irrelevant, but they do not displace the treaty structure. Part III assumes that straits are sensitive spaces and still denies bordering States the power to suspend passage. The legal question is therefore never just whether a State invokes security. It is whether the measure adopted remains within the narrow regulatory authority recognized by the Convention (Churchill, Lowe and Sander, 2022).

2.3 The residual place of innocent passage

Innocent passage still has a place in the analysis, although it is not the dominant regime for Hormuz if Part III applies. It remains relevant for two reasons. First, Iran’s legal position depends on resisting the full transit-passage framework and pushing the analysis toward a narrower regime. Second, innocent passage remains part of the historical development of straits law and helps explain why the modern law took its present form (Lowe, 1967; Corfu Channel 1949).

Under the law of innocent passage, the coastal State has greater scope to regulate conduct in its territorial sea. Passage must be innocent, meaning it must not be prejudicial to the peace, good order, or security of the coastal State. That framework is more restrictive than transit passage and gives the coastal State more room to react to activities it considers threatening (UNCLOS, 1982, arts 17–19).

Even so, innocent passage does not support the arbitrary denial of movement through an international strait. UNCLOS itself preserves non-suspension in the straits covered by Article 45, where the applicable regime remains innocent passage rather than transit passage. The Convention therefore recognizes that, even under a narrower framework, passage through certain international straits cannot simply be switched off by unilateral coastal decision (UNCLOS, 1982, art. 45).

The pre-UNCLOS jurisprudence points in the same direction. In Corfu Channel, the International Court of Justice held that States in peacetime had a right to send warships through straits used for international navigation without prior authorization from the coastal State. The case did not articulate the later doctrine of transit passage, but it rejected the idea that an international strait could be treated as a space of complete coastal discretion (Corfu Channel 1949, p. 28).

That is why innocent passage matters here only as a secondary line of analysis. It may narrow some aspects of the legal debate, especially where Iran argues that transit passage is a treaty-based regime unavailable against a non-party. It does not solve Iran’s larger problem. Even under a narrower approach, international law has long been hostile to the arbitrary prohibition of passage through waterways that function as essential routes of international navigation (O’Connell, 1984; Churchill, Lowe and Sander, 2022).

3. Does the Transit Passage Regime Bind Iran?

3.1 Iran’s non-ratification of UNCLOS

The treaty position must be stated carefully. Iran signed the United Nations Convention on the Law of the Sea on 10 December 1982, but it did not ratify the Convention (United Nations, 2026). That point matters because a serious legal analysis cannot move directly from the text of the Convention to the conclusion that Iran has breached it. Before any allegation of treaty violation is made, the article must confront the prior question of legal opposability.

This is where the discussion becomes genuinely academic. Treaty law and customary international law are not the same source of obligation, and they must not be treated as if they were interchangeable. A non-party is not bound by a treaty simply because the treaty is widely accepted or widely cited. The real question, therefore, is not only what UNCLOS says, but which parts of the relevant navigational regime can be invoked against Iran independently of ratification (International Law Commission, 2016).

That distinction is not formalism. It affects the entire structure of the argument. If the article fails to separate treaty obligation from customary obligation, it will overstate its conclusion and weaken its credibility. A precise analysis must therefore begin by recognizing that Iran’s non-ratification is not a marginal detail, but one of the central legal facts of the dispute (United Nations, 2026).

3.2 Iran’s 1982 declaration and the package-deal argument

Iran’s strongest defense appears in its declaration made upon signature. In that declaration, Iran stated that some provisions of the Convention were products of quid pro quo and did not necessarily reflect pre-existing customary law. It also stated that only States parties should be entitled to benefit from the “contractual rights” created by the Convention, and it referred expressly to transit passage through straits used for international navigation (Iran, 1982).

This argument matters because it challenges the source of the legal rule itself. Iran is not only denying that a restriction of passage would be unlawful. It is asserting that the specific rule of transit passage, in its full Convention form, cannot automatically be applied against a State that never accepted the treaty bargain. That is a much stronger argument than a simple appeal to sovereignty, and it must be addressed directly rather than ignored.

The declaration also reveals the deeper structure of Iran’s legal position. Iran linked the question of passage to the coastal State's security rights and maintained that, under its understanding of the law, prior authorization could be required for warships exercising innocent passage in the territorial sea (Iran, 1982). This shows that Iran’s resistance to an unrestricted transit regime is not recent. It has been framed for decades as a question of source, reciprocity, and coastal security.

3.3 Iran’s 1993 Marine Areas Law

Iran’s 1993 Law of Marine Areas supports that reading. The law governs maritime spaces in the Persian Gulf, the Strait of Hormuz, and the Oman Sea, and it uses the language of “harmless passing” rather than the broader language of transit passage (Iran, 1993). That legislative choice is important because it reflects a narrower and more security-oriented conception of foreign navigation in waters adjacent to Iran.

The law also grants the Iranian authorities a substantial degree of control. It authorizes suspension of passage in areas of the territorial sea for reasons connected to security and the higher interests of the State. It further requires prior approval for certain categories of vessels, including warships, submarines, ships carrying nuclear fuel, ships carrying dangerous substances, and foreign fishing vessels (Iran, 1993). These provisions are consistent with a legal approach that resists the idea of automatic passage beyond meaningful coastal supervision.

Domestic legislation does not decide the content of international law. Iran cannot unilaterally define the international regime of Hormuz by enacting a national statute. But the 1993 law remains legally relevant because it demonstrates continuity. It shows that Iran’s current position is not improvised or opportunistic. It rests on a long-standing legal posture that treats passage in and near Hormuz through the framework of innocent passage, prior control, and national security.

3.4 Transit passage and customary international law

The hardest issue is whether the core of the transit passage regime binds Iran as customary international law. That question should be answered with caution. It is not enough to point out that the rule appears in a major multilateral convention. A treaty rule may codify an older custom, crystallize an emerging one, or remain essentially treaty-based. That must be demonstrated through legal analysis, not assumed from the text alone (International Law Commission, 2016).

For that reason, the strongest customary argument is narrower than the full Convention regime. The more defensible claim is not that every element of modern transit passage applies to Iran word for word. It is that international law has long rejected the idea that a State bordering an international strait may arbitrarily close it to world navigation. That narrower proposition has firmer foundations in case law and general legal principle.

The leading authority remains the Corfu Channel. In that case, the International Court of Justice held that States in time of peace had a right to send warships through straits used for international navigation between two parts of the high seas without prior authorization, provided that passage was innocent. The Court further stated that, unless an international convention provided otherwise, a coastal State had no right to prohibit such passage in time of peace (Corfu Channel, 1949). Although the judgment predates the modern formulation of transit passage, it clearly rejects complete coastal discretion over an international strait.

That point should shape the tone of the article. It is possible to argue that the full modern regime remains contested as custom when invoked against Iran. It is much easier to argue that a narrower customary rule exists against the arbitrary closure or unilateral prohibition of passage through an international strait used by the international community. A careful writer should preserve that distinction, because it makes the argument stronger rather than weaker.

3.5 Persistent objection and its limits

Once the customary-law issue is raised, Iran can invoke the doctrine of persistent objection. Under that doctrine, a State that clearly and consistently objects to an emerging rule of customary international law while the rule is forming may avoid being bound by it. The objection must be public, sufficiently clear, and maintained over time. It is not enough to object late or vaguely, and the burden lies on the State relying on the doctrine (International Law Commission, 2016).

Iran does have material supporting that line of argument. Its 1982 declaration openly rejected the automatic extension of transit passage to non-parties, and its 1993 legislation continued to regulate passage through a narrower and more restrictive framework. Those acts show that Iran did not remain silent while the modern law of straits developed. On the contrary, it expressed resistance in legal terms and maintained that resistance in domestic legislation (Iran, 1982; Iran, 1993).

Even so, the doctrine has limits, and those limits matter here. Persistent objection is easier to argue against a highly specific treaty-derived formulation than against a narrower rule with older customary roots. Iran’s case is therefore stronger if the claim made against it is that the entire modern transit passage regime binds it in full. Its case is weaker if the claim is that international law, even apart from the Convention, does not allow a State to arbitrarily close an international strait used for international navigation.

The most careful conclusion is therefore a layered one. Iran has a serious argument against the automatic application of the entire modern transit passage regime as treaty law or wholesale custom. It has a weaker argument against the narrower proposition that Hormuz cannot lawfully be turned into a discretionary permission system or closed arbitrarily to international shipping. That distinction should remain central to the article, because it captures the real legal difficulty without overstating either side.

4. The Jurisprudence on Straits, Mines, and Maritime Force

4.1 Corfu Channel and the law of international straits

The historical starting point is the Corfu Channel. The International Court of Justice did not use the later language of transit passage, but it established the older customary logic on which much of the modern law of straits rests. The Court examined the North Corfu Channel as a waterway connecting two parts of the high seas and looked not only at geography, but also at actual use. Because the channel was regularly used for international navigation, the Court treated it as belonging to the class of international highways through which passage could not be prohibited by the coastal State in time of peace (Corfu Channel, 1949).

That holding matters far beyond the facts of the case. The Court recognized that States in time of peace had a right to send warships through such a strait without previous authorization, provided that passage was innocent. The value of Corfu Channel is therefore not that it reproduces modern straits doctrine in its present form. Its value lies in something more basic: it rejects the claim that an international strait may be reduced to a zone of unilateral coastal discretion simply because part of it lies within territorial waters. That older rule is central to Hormuz because it supports the narrower customary proposition that international passage through a strait cannot be arbitrarily prohibited (Corfu Channel, 1949).

4.2 Nicaragua and interference with maritime commerce

Nicaragua is relevant for a different reason. It is not primarily a straits case, and it should not be used as one. Its importance lies in the Court’s treatment of coercive maritime interference, especially mining. The Court held that the mining of Nicaraguan ports by the United States was a breach of the customary prohibition on the use of force, and it also treated such conduct as part of an unlawful pattern of intervention in Nicaragua’s affairs (Nicaragua, 1986).

For the present article, the narrower lesson is the important one. Mining and comparable interference with peaceful maritime activity are not legally neutral acts. They affect navigation, threaten civilian and commercial shipping, and may violate customary rules independently of treaty participation. The Court also gave weight to the failure to notify the existence and location of mines, drawing support from broader humanitarian and navigational principles reflected in the law of naval warfare. That point matters for Hormuz because any attempt to obstruct maritime traffic by force, by mines, or by comparable coercive means raises legal issues that go well beyond ordinary regulation of passage (Nicaragua, 1986).

4.3 Oil Platforms and the discipline of self-defense

Oil Platforms is the most important case for the later sections of this article because it places the legal debate in the Persian Gulf itself. The Court was not deciding a general freedom-of-navigation claim under the law of the sea. It was applying the 1955 Treaty of Amity between Iran and the United States. Even so, the judgment is crucial because it shows how strictly international law examines claims of maritime self-defense in a security crisis. The Court scrutinized the evidence, the alleged armed attacks, and the relationship between the incident invoked and the force used in response (Oil Platforms, 2003).

The judgment is especially useful because it resists loose strategic reasoning. The Court treated the evidence concerning Iranian responsibility for the mining of the USS Samuel B. Roberts as highly suggestive but not conclusive, and it held that the United States had not shown that its attacks on Iranian oil platforms were necessary measures to protect its essential security interests. The broader implication is clear. Even where a State invokes grave security threats in the Gulf, the legal standard does not relax into political discretion. Proof, necessity, and proportionality still matter. That is why Oil Platforms supports a later argument that a broad closure of Hormuz would be much harder to justify than a narrow defensive response directed at a specific armed attack (Oil Platforms, 2003).

4.4 The supporting role of later maritime case law

Later maritime case law does not replace these three judgments, but it reinforces the same pattern. In ARA Libertad, the International Tribunal for the Law of the Sea ordered the release of an Argentine warship detained by Ghana and reaffirmed the strength of sovereign immunity for warships. That case matters here because it confirms that coastal enforcement at sea is not unlimited, even where the coastal State invokes domestic legal process or security concerns. Maritime space remains governed by international constraints that cannot be displaced by unilateral assertion (ARA Libertad, 2012).

A similar point appears in the provisional measures order in the case concerning the detention of three Ukrainian naval vessels. The Tribunal treated the dispute as justiciable, notwithstanding the security language surrounding the incident, and ordered the release of the naval vessels and their servicemen. The lesson is modest but important. Maritime disputes do not become immune from legal scrutiny merely because one side describes the situation in strategic or military terms. Later tribunal practice therefore supports the broader line already visible in Corfu Channel, Nicaragua, and Oil Platforms: navigational rights, coastal enforcement, and maritime security remain matters of law, not pure discretion (Ukraine v Russian Federation, 2019).

5. Can Iran Lawfully Close or Restrict the Strait?

5.1 Total closure

The clearest point concerns a total closure. If the Strait of Hormuz is governed by the regime of transit passage, a complete closure is prima facie incompatible with that regime. The reason is straightforward. The governing rules were designed to prevent a State bordering a narrow international chokepoint from suspending passage whenever a political or military crisis arises. Under that framework, the question is not simply whether Iran faces serious security threats. The real question is whether those threats allow Iran to suspend a regime whose central purpose is to keep international transit open (UNCLOS, 1982, arts 38 and 44).

A total closure is difficult to defend because it goes beyond regulation and reaches the level of legal exclusion. A coastal State may regulate navigation for limited purposes, but a full prohibition on passage changes the nature of the strait itself. It turns an international corridor into a space of discretionary control. That is precisely what the modern law of straits seeks to avoid, and it is why Article 44 is so central. The prohibition on hampering and suspending passage is not secondary language. It is the doctrinal core of the regime (Churchill, Lowe and Sander, 2022; Rothwell and Stephens, 2016).

Iran may answer that security emergencies cannot be ignored, especially in conditions of armed conflict. That is true as a general proposition, but it does not solve the legal problem. Even a serious threat does not automatically authorize the suspension of passage through an international strait. A State invoking self-defense must still show that the measures adopted are necessary and proportionate. A total closure affecting the entire corridor is therefore much harder to justify than a narrowly tailored defensive response directed at a specific and immediate threat (Oil Platforms, 2003).

The position is slightly more complex if one brackets the full treaty regime and argues only from customary international law. Even then, the legal case for a total closure remains weak. The older customary logic reflected in the Corfu Channel does not support the unilateral prohibition of passage through an international strait used by the international community. So, while the argument is strongest under the modern regime of transit passage, the narrower customary argument also points against a lawful total closure (Corfu Channel, 1949).

5.2 Selective closure and discriminatory passage

The more sophisticated Iranian position is not always an open declaration of total closure. It is the claim that passage remains available for “non-hostile” vessels while being restricted or denied to vessels linked to hostile States or hostile operations. Legally, that position may be more attractive than a formal closure, but it remains difficult to sustain. A selective restriction can still amount to a suspension of passage for the States and vessels against which it is directed.

This point follows from the structure of the Straits Law. The relevant rules do not only prohibit formal suspension. They also prohibit measures that hamper or impair passage and laws that discriminate in form or in fact among foreign ships. A selective system that allows some States to pass while excluding others does not escape that rule merely because some traffic still moves. For the targeted vessels, the practical effect may be indistinguishable from suspension (UNCLOS, 1982, arts 42 and 44).

This makes selective closure analytically more important than total closure. Total closure is the easier case. Selective passage is where a coastal State tries to present coercive exclusion as regulation. Yet the legal difficulty remains serious. Once the bordering State decides that passage depends on its own political classification of foreign vessels as hostile or non-hostile, the right of passage begins to look less like a legal entitlement and more like a privilege granted by the coastal authority. That is precisely the shift the law of straits was designed to prevent (Churchill, Lowe and Sander, 2022).

Iran might argue that hostile vessels are not situated in the same way as neutral vessels and that differential treatment is therefore justified. That argument has some force in a context of real hostilities, but it does not remove the problem. First, the category of “hostile” may be framed too broadly and may reach commercial shipping with no direct military function. Second, measures that affect neutral commerce and third-State vessels raise additional legal concerns under both the law of the sea and the law governing the use of force. A discriminatory passage regime is therefore not a minor variation on ordinary regulation. It is a serious legal departure from the idea of open transit through an international strait (UN Security Council, 1984; UN Security Council, 2026).

5.3 Prior coordination, authorization, and escort schemes

Not every requirement imposed on transiting vessels is unlawful. International navigation often depends on traffic separation schemes, reporting arrangements, and safety measures designed to reduce collision risks in narrow waterways. A serious analysis must recognize that point. The law of straits does not prohibit all regulation. It prohibits regulation that, in substance, subordinates passage to the discretionary control of the bordering State (UNCLOS, 1982, arts 41 and 42).

That distinction is crucial for Hormuz. Prior coordination may be lawful if it operates as a neutral navigational arrangement tied to safety and applied without discrimination. The same is true of voluntary escort systems or communication measures that assist secure transit. The unlawfulness appears when a right of passage is transformed into a permission system. If vessels must obtain approval, accept political vetting, or submit to conditions that allow Iran to decide, case by case, who may pass, the measure moves beyond regulation and becomes control (Rothwell and Stephens, 2016).

The practical effect test is therefore decisive. A measure described as “coordination” may still be unlawful if refusal to coordinate leads to exclusion, detention, or coercive interception. The same applies to mandatory escort schemes. If an escort requirement is truly a neutral safety device, it may be defensible. If it functions as a compulsory mechanism through which Iran supervises, delays, or selectively permits passage, it becomes much harder to reconcile with the legal structure of international straits. The issue is not the label attached to the measure, but the way it operates in practice (UNCLOS, 1982, art. 42).

Iran’s own legal posture makes this subsection especially important. Its 1982 declaration and 1993 legislation show a long-standing preference for prior authorization and security-sensitive control over certain categories of foreign vessels. That history explains why coordination measures in Hormuz cannot be assessed innocently at face value. In this setting, the central legal question is always whether regulation serves navigation or whether it places navigation under Iranian discretion (Iran, 1982; Iran, 1993).

5.4 Mines, threats, and attacks on civilian shipping

The legal case against coercive interference is even stronger when the conduct moves beyond regulatory measures and enters the realm of force. Mining a maritime corridor, broadcasting threats to passing ships, or attacking merchant vessels cannot be assessed only through the law of straits. Those acts also engage the prohibition on the use of force, the protection of civilian shipping, and, where armed conflict exists, the law applicable to hostilities at sea (Nicaragua, 1986).

Mining is especially difficult to defend. In Nicaragua, the International Court of Justice treated the mining of ports as a breach of customary international law and emphasized that maritime interference of that kind is not a legally neutral act. The Court also gave importance to the failure to notify the presence of mines. In a narrow and heavily used waterway such as Hormuz, mining or comparable obstruction would therefore raise legal concerns even apart from the treaty law of transit passage. It directly endangers civilian navigation and international commerce (Nicaragua, 1986).

Threats and attacks against merchant shipping create a similar problem. A broadcast warning that all or most vessels risk attack is not easily reconcilable with a regime built on secure international passage. If actual attacks follow, the legal difficulty becomes even greater. During periods of armed conflict, some maritime uses of force may be lawful, but that does not create a free zone for coercion against commercial traffic. Neutral shipping, civilian crews, and third-State commerce remain legally protected categories, and broad or indiscriminate interference with them is highly vulnerable under international law (UN Security Council, 1984; UN Security Council, 1987).

This is one of the strongest parts of the argument against a lawful Strait of Hormuz closure. The regime question may be debated at the margins when the issue is treaty status or the exact scope of customary law. Violent interference with civilian or neutral shipping is harder to defend. Even if one accepted that Iran contests the full treaty basis of transit passage, mining, threats against merchant vessels, and attacks on civilian shipping would still face serious legal obstacles under the general law on force, maritime security, and the protection of peaceful navigation (Nicaragua, 1986; Oil Platforms, 2003).

6. Self-Defense, Naval Warfare, and Neutral Shipping

6.1 Iran’s self-defense claim

Iran’s strongest legal position begins with Article 51 of the United Nations Charter. If Iran argues that it is responding to an armed attack against its territory, forces, or essential installations, that claim cannot be dismissed out of hand. Public international law does recognize an inherent right of self-defense when an armed attack occurs, and any serious analysis must concede that the legal relevance of Article 51 is real rather than rhetorical (UN Charter, 1945, art. 51).

That point matters because a weak article would treat every Iranian measure in Hormuz as legally identical from the outset. They are not. A narrowly tailored defensive response to an immediate military threat is different from a general policy affecting all or most traffic through the strait. International law does not prevent a State from invoking self-defense at sea, but it does require that the measure adopted be connected to a concrete defensive purpose rather than to broad strategic pressure (Oil Platforms, 2003).

The discipline of self-defense is therefore decisive. Even where a State has suffered or claims to have suffered an armed attack, the response must satisfy necessity and proportionality. Necessity asks whether the measure was required to repel or prevent the attack. Proportionality asks whether the scope and effects of the response remain tied to that defensive aim. Those requirements do not disappear merely because the setting is maritime or because the State invoking them faces a serious security crisis (Nicaragua, 1986; Oil Platforms, 2003).

This is why self-defense does not automatically displace the law of straits. Iran may argue that security conditions justify exceptional action in Hormuz, but that does not mean the strait becomes a legal vacuum. The right of self-defense operates within international law; it does not erase other relevant rules. The stronger Iranian position is therefore not that all restrictions become lawful once hostilities exist, but that some narrowly framed defensive measures may be justified if they are strictly necessary and proportionate.

6.2 Why self-defense does not easily justify a strait closure

A closure or near-closure of the Strait of Hormuz is much harder to defend than a limited and specific defensive action. The problem is scale. Hormuz is not an ordinary maritime zone used mainly by the coastal State. It is a narrow international corridor through which third-State shipping, civilian crews, energy cargoes, and global trade pass in large volume. A measure that broadly blocks or chills transit, therefore, affects a far wider set of actors than the alleged attacker alone (UNCLOS, 1982, arts 38 and 44).

That broad impact weakens the self-defense argument. A response directed at a specific military threat may sometimes be defended as proportionate. A response that places an entire chokepoint under coercive restriction is far more difficult to reconcile with the idea of proportionate defense. The more general the measure becomes, the further it moves away from immediate protection and the closer it comes to strategic leverage. International law is far less tolerant of that second type of conduct (Oil Platforms, 2003).

The same point can be made in terms of necessity. To justify a sweeping restriction, Iran would have to show not only that it faced a real armed attack, but also that obstructing a major international strait was necessary to repel or prevent that attack. That is a demanding test. It is much easier to justify a narrowly targeted operational measure than a general interference with commercial navigation through one of the world’s principal maritime chokepoints (Nicaragua, 1986; Greenwood, 2003).

For that reason, self-defense becomes less persuasive as the measure becomes more indiscriminate. A temporary response tied to a concrete threat is one thing. A broad closure, a generalized threat to shipping, or a system that conditions passage on political alignment is another. Once the effects spread to neutral traffic and third-State commerce on a large scale, the claim of proportionate defense becomes much harder to sustain.

6.3 Neutral shipping and the law of armed conflict at sea

Even if the situation is characterized as an armed conflict, neutral commercial shipping does not lose legal significance. The law of armed conflict at sea does not treat all merchant traffic as an undifferentiated target. Neutral vessels remain protected by important rules, and interference with them must be justified within a structured legal framework rather than by broad assertions of maritime danger (Hague Convention XIII, 1907; San Remo Manual, 1994).

This is where careless use of blockade language should be avoided. A blockade is a specific legal institution with demanding conditions, including declaration, effectiveness, non-discrimination among neutral States, and compliance with the wider law of armed conflict. An article that casually describes Iranian conduct as a blockade without analyzing those requirements will weaken its own legal precision. The better approach is to say that broad interference with neutral merchant traffic remains legally fraught even in wartime unless the strict conditions of the law of naval warfare are met (San Remo Manual, 1994, paras 93–104).

Neutral rights matter because they expose the limits of a generalized closure theory. A measure directed against enemy military operations may, in some circumstances, be arguable. A measure that endangers or excludes neutral shipping on a wide scale is much harder to defend. This is especially true where the vessels concerned are engaged in ordinary commercial navigation and are not shown to be carrying contraband, breaching a lawful blockade, or directly participating in hostilities (Hague Convention XIII, 1907; Doswald-Beck, 1995).

The legal significance of neutral shipping, therefore, reinforces the broader conclusion of this article. Even in conditions of armed conflict, Hormuz cannot easily be transformed into a zone where the coastal State determines, by force or threat, which merchant vessels may continue to pass. The more Iranian measures affect neutral commerce in general terms, the weaker the defense grounded in Article 51 and the law of naval warfare becomes.

Also Read

• USA-Iran War and the Use of Force under International Law

• Self-Defense in International Law

• The Principle of Proportionality in International Law

• Neutrality in International Law

• Customary International Law: How It Forms and Works

• Principle of Territorial Integrity in International Law

• Principle of Sovereign Equality of States

• The Implications of the Iran War

7. The Role of the United Nations and Contemporary Institutional Practice

7.1 Resolution 552 and the older Gulf precedent

The United Nations practice on Gulf shipping did not begin in 2026. Security Council Resolution 552, adopted on 1 June 1984, treated attacks on commercial ships in the Gulf as a matter of international peace and security and responded in language that remains legally relevant today. The Council called upon all States to respect the right of free navigation, reaffirmed free navigation in international waters and sea lanes for shipping en route to and from the ports and installations of littoral States not party to the hostilities, condemned the attacks on commercial ships bound to and from Kuwait and Saudi Arabia, and demanded that such attacks cease immediately (UN Security Council, 1984).

The importance of Resolution 552 is historical continuity. It shows that interference with commercial shipping in the Gulf has long been framed by the Council not as a purely regional quarrel, but as a threat with wider legal and systemic implications. That does not by itself settle the exact content of customary straits law. It does, however, provide strong institutional evidence that attacks on commercial shipping and interference with non-belligerent maritime traffic in the Gulf have been viewed for decades as matters that engage the collective security framework of the Charter (UN Security Council, 1984).

7.2 Resolution 598 and the condemnation of attacks at sea

Resolution 598, adopted unanimously on 20 July 1987 during the Iran-Iraq war, reinforces that older pattern. The resolution is wider in scope because it addressed the war as a whole, but it is still useful for present purposes because it expressly deplored attacks on neutral shipping and civilian aircraft, alongside violations of international humanitarian law and other laws of armed conflict (UN Security Council, 1987).

This resolution should not be used as a substitute for the law of straits. Its function is narrower. It confirms that the Council’s concern with maritime violence in the Gulf has long included neutral shipping and civilian traffic. In other words, contemporary disputes over Hormuz are not legally unprecedented. They sit within a longer institutional record in which attacks at sea, especially those affecting non-belligerent shipping, have been treated as a serious international legal problem (UN Security Council, 1987).

7.3 Resolution 2817 and the 2026 institutional response

Resolution 2817, adopted on 11 March 2026 by 13 votes with two abstentions, is the most important contemporary Security Council text for this article. The resolution recalls Resolution 552, situates the events in and around Hormuz within the Council’s responsibility for international peace and security, and condemns actions or threats by Iran aimed at closing or obstructing international navigation through the Strait of Hormuz. It therefore places the dispute squarely within the language of maritime security, international navigation, and wider systemic risk rather than treating it as a purely bilateral matter (UN Security Council, 2026).

Its importance should still be stated carefully. Resolution 2817 does not end the doctrinal debate over whether the full modern regime of transit passage binds Iran as treaty law or customary law. Security Council practice is not a shortcut that dissolves all questions of source. Its significance lies elsewhere. It is powerful contemporary evidence of institutional condemnation and of the Council’s view that attacks, threats, and obstruction affecting navigation through Hormuz are matters of international peace and security with consequences extending well beyond the immediate parties (UN Security Council, 2026).

7.4 IMO practice and the language of freedom of navigation

The International Maritime Organization adds a specialized institutional perspective. On 1 March 2026, the IMO Secretary-General stated that no attack on innocent seafarers or civilian shipping is ever justified and described freedom of navigation as a fundamental principle of international maritime law. That statement was followed by an extraordinary session of the IMO Council on 18–19 March 2026, after requests from several Member States, specifically to address the effects of the crisis on shipping and seafarers in and around the Strait of Hormuz (IMO, 2026a; IMO, 2026b).

The Council’s response is legally useful even though it is not a binding adjudication. It strongly condemned the threats and attacks against vessels and the purported closure of the Strait of Hormuz, reiterated that navigational rights and freedoms of merchant and commercial vessels in accordance with international law must be respected, and called for an internationally coordinated safe-passage framework. It also focused on civilian seafarers, supply access, crew changes, and the practical dangers created by attacks, jamming, and the confinement of ships in the Gulf region (IMO, 2026c).

IMO, practice therefore supports the broader legal argument of this article in a specific way. It does not determine the full content of customary law, and it does not replace the treaty and case-law analysis. What it does provide is contemporary institutional practice from the specialized global maritime body most directly concerned with merchant shipping, navigational safety, and seafarer welfare. That practice consistently uses the language of navigational rights and freedoms, civilian protection, and coordinated safe passage, which sits uneasily with any theory of broad or coercive closure of Hormuz (IMO, 2026a; IMO, 2026c).

8. Conclusion

The legal issue is not best framed as a clash between Iranian sovereignty and abstract freedom of navigation. That formulation is too crude. The real issue is whether a State bordering an international strait may respond to crisis by placing a globally significant route under its own discretionary control. On that question, the weight of international law runs against Iran. The modern law of straits was built to prevent chokepoint coercion, and the older customary law reflected in Corfu Channel also points away from unilateral prohibition of passage through an international strait (Corfu Channel, 1949; UNCLOS, 1982).

That does not mean every legal question is easy. The weakest part of the case against Iran is the claim that the whole modern transit-passage regime binds it automatically in the same way it binds States parties to UNCLOS. Iran has a serious argument about the source. Its non-party status, its 1982 declaration, and its 1993 legislation show a long-standing refusal to accept the full transit-passage package as automatically opposable. Any rigorous analysis must acknowledge that point, because the dispute is partly about the content of the rule, but also about the legal basis on which that rule is invoked against Iran (Iran, 1982; Iran, 1993).

Even so, Iran’s stronger arguments do not carry it as far as it needs. They may complicate the treaty analysis, but they do not make a broad restriction lawful. A total closure of Hormuz remains exceptionally difficult to defend. A selective regime allowing passage only for vessels deemed “non-hostile” is also deeply vulnerable, because it transforms a legal right of passage into a system of political screening. At that point, the measure is no longer merely regulatory. It becomes a form of coercive control over an international corridor, which is precisely what the law of straits was designed to restrain (UNCLOS, 1982, arts 42 and 44).

The same conclusion follows from the law of self-defense. Article 51 is relevant, and it would be wrong to write as if it were not. A State responding to an armed attack is not deprived of legal defenses simply because the response takes place at sea. But self-defense does not dissolve the rest of the legal order. Necessity and proportionality remain the controlling standards, and those standards become harder to satisfy as the measure grows broader, affects neutral shipping, and disrupts third-State commerce on a large scale. A narrow response to a concrete military threat may be arguable. A sweeping restriction on passage through Hormuz is much harder to reconcile with those requirements (Nicaragua, 1986; Oil Platforms, 2003).

The most defensible conclusion, therefore, is a layered one. Iran has credible arguments against the automatic application of the entire UNCLOS transit-passage regime. It has weaker arguments against the narrower proposition that it cannot lawfully close Hormuz, materially obstruct it, or subject passage through it to broad discretionary control. That is why the legal answer is serious without being indeterminate. The controversy is not simplistic, but neither is it balanced evenly. Once the analysis moves from formal claims of sovereignty to the actual legal tests governing straits, force, and neutral shipping, the case for a lawful Iranian closure becomes very difficult to sustain.

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