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

1. Introduction

The USA-Iran War of 2026 represents one of the most significant interstate confrontations of the contemporary era and a direct test of the legal framework governing the use of force. The conflict began on 28 February 2026 with coordinated military strikes conducted by the United States and Israel against targets within Iranian territory. These operations marked the transition from prolonged geopolitical tension to open armed hostilities between sovereign States.

At the centre of the legal analysis lies a fundamental question: did the initial resort to force comply with the United Nations Charter, or did it breach the prohibition contained in Article 2(4)? The Charter establishes a general ban on the threat or use of force against the territorial integrity or political independence of any State (United Nations, 1945). This rule is widely recognised as a cornerstone of contemporary international law and reflects both treaty and customary norms (Brownlie, 1963; Gray, 2018).

Only narrow exceptions permit departure from this prohibition. Force may be authorised by the Security Council under Chapter VII, exercised in individual or collective self-defence under Article 51, or undertaken with the valid consent of the territorial State. In the absence of one of these legal bases, cross-border military action remains unlawful. Political hostility, long-standing rivalry, or strategic distrust do not create independent exceptions to the Charter framework.

The 2026 hostilities, therefore, require a structured legal assessment. Public statements accompanying the opening strikes referred to security threats and strategic risks. International law, however, requires objective criteria. The existence of an armed attack, its attribution to a State, and compliance with necessity and proportionality standards are decisive elements (ICJ, 1986; Dinstein, 2017). Rhetorical characterisation does not determine legality.

The conflict also raises broader doctrinal issues. Questions of anticipatory self-defence, proxy warfare, maritime operations, and cyber activities all feature in the 2026 escalation. These dimensions do not displace the Charter’s core rules but require their application in complex operational contexts. The jurisprudence of the International Court of Justice, including its insistence on strict interpretation of self-defence, provides an important analytical baseline (ICJ, 2003).

This article proceeds on three methodological commitments. First, it anchors the analysis in positive international law: treaty provisions, customary norms, and judicial decisions. Second, it separates facts from contested political narratives. Third, it maintains the distinction between jus ad bellum, governing the legality of resort to force, and jus in bello, governing the conduct of hostilities once armed conflict exists.

The 2026 confrontation serves as a contemporary case study of the resilience and limits of the UN Charter system. It tests whether the prohibition of force continues to function as a meaningful constraint in situations involving major military powers. The sections that follow examine the legality of the initial resort to force, the scope of self-defence claims, the role of collective security mechanisms and the consequences of any violations under international law.

2. Factual and Legal Characterization of the 2026 Conflict

The USA-Iran War began on 28 February 2026 with coordinated military strikes carried out by the United States and Israel against targets within Iranian territory. The United States designated its campaign Operation Epic Fury, and Israel referred to its parallel actions as Operation Roaring Lion. These operations constitute the factual starting point for legal analysis.

The opening phase involved aerial bombardment and missile strikes directed at cities including Tehran, Isfahan, Qom, and Karaj. Reported targets included military infrastructure, command facilities, and strategic installations. The strikes were conducted by regular armed forces across internationally recognised borders. No Security Council authorisation preceded these operations.

These facts establish the minimum elements required for legal assessment. First, there was a cross-border use of armed force. Second, the initiating actors were identifiable States. Third, the scale of operations extended beyond isolated or accidental incidents. The coordinated and multi-site character of the strikes indicates organised military action rather than sporadic exchanges.

Following the initial strikes, Iran launched retaliatory missile and drone attacks against military installations associated with the United States and Israel in the region. These actions were also cross-border uses of force. The reciprocal nature of the operations marked the beginning of sustained inter-State hostilities.

The conflict also developed maritime and technological dimensions. Heightened naval activity occurred in the Persian Gulf, including operations involving military vessels. Attacks on warships or naval assets are legally significant because they may constitute armed attacks depending on scale and consequences (Dinstein, 2017). In parallel, cyber operations were reportedly conducted alongside kinetic strikes. For legal purposes, cyber activities are relevant only if their scale and effects are comparable to conventional uses of force (Schmitt, 2017).

Public statements by the parties referenced national security concerns and strategic objectives. These declarations form part of the factual background. However, political rhetoric does not determine legality. The legally relevant facts concern the occurrence of force, its scale, its attribution, and its cross-border character. Jurisprudence has consistently required objective assessment of such elements (ICJ, 1986).

2.1 Triggering Incident and Escalation

The first legally relevant use of large-scale force occurred on 28 February 2026 with the coordinated strikes under Operation Epic Fury and Operation Roaring Lion. This event represents the initial kinetic escalation between the parties.

The United States and Israel framed their actions as responsive to security threats. Iran characterised the strikes as unlawful aggression and responded with missile and drone attacks against military targets. The legal question is whether the escalation followed a prior armed attack of sufficient gravity or whether it began with the February 28 operations.

Under international law, only a grave armed attack triggers the right of self-defence (ICJ, 1986). If no such attack occurred prior to 28 February, the initial strikes cannot be characterised as reactive in the strict legal sense. The sequence of events is therefore central to determining which State first resorted to force within the meaning of Article 2(4) of the UN Charter (United Nations, 1945).

2.2 Nature of the Conflict

Once reciprocal missile and aerial strikes occurred between regular armed forces of sovereign States, the situation qualified as an international armed conflict. Common Article 2 of the 1949 Geneva Conventions provides that any armed conflict between two or more High Contracting Parties triggers the application of international humanitarian law, regardless of formal declarations (United Nations, 1949).

The 2026 hostilities involved direct military exchanges between State forces across recognised borders. This satisfies the inter-State criterion for classification as an international armed conflict. That classification activates the legal framework governing conduct of hostilities, protection of civilians, and treatment of prisoners.

This characterisation does not determine whether the resort to force was lawful under jus ad bellum. It establishes only that, once hostilities commenced, the law of armed conflict applied alongside the Charter framework regulating the legality of force.

3. Article 2(4) UN Charter: Prohibition of Force

Article 2(4) of the United Nations Charter establishes a general prohibition on the threat or use of force against the territorial integrity or political independence of any State (United Nations, 1945). This rule is widely recognised as a cornerstone of the contemporary international legal order and reflects both treaty law and customary international law (Brownlie, 1963; Gray, 2018). The prohibition is not conditional upon political context, strategic tension or regional instability. It applies irrespective of the perceived hostility between States.

Any cross-border military strike constitutes a prima facie breach of Article 2(4). Aerial bombardment, missile launches, and coordinated military operations directed at the territory of another sovereign State fall squarely within the ordinary meaning of “use of force.” In the context of the USA-Iran War, the coordinated strikes carried out on 28 February 2026 under Operation Epic Fury and Operation Roaring Lion therefore engage Article 2(4) at the outset. The fact that the targets were military rather than civilian does not remove the conduct from the scope of the prohibition. The Charter regulates the resort to force, not merely its humanitarian consequences.

The prohibition in Article 2(4) is comprehensive but not absolute. International law recognises three narrow pathways through which a cross-border use of force may avoid unlawfulness. First, force may be authorised by the Security Council acting under Chapter VII of the Charter. Such authorisation must be explicit and based on a determination of a threat to the peace, breach of the peace or act of aggression. Second, force may be exercised in individual or collective self-defence under Article 51, provided the strict conditions of that provision are met. Third, military operations conducted with the valid consent of the territorial State do not violate its sovereignty and therefore fall outside the prohibition (Crawford, 2019).

Absent one of these recognised bases, a cross-border force remains unlawful. Political hostility, long-standing rivalry, or strategic mistrust do not constitute independent legal grounds for the use of force. The Charter does not recognise a doctrine of preventive war based on anticipated future capabilities. Nor does it permit unilateral enforcement of international norms through armed force in the absence of Security Council authorisation. The International Court of Justice has repeatedly affirmed that the prohibition of force is a fundamental principle of international law and that exceptions must be interpreted restrictively (ICJ, 1986; ICJ, 2003).

In the 2026 context, no Security Council resolution authorised the initial strikes against Iran. The legal assessment, therefore, turns on whether the operations can be justified under self-defence or another recognised exception. Until such justification is established, the February 28 cross-border strikes remain prima facie incompatible with Article 2(4).

The prohibition of force also protects the structural integrity of the international system. It embodies the principle of sovereign equality and preserves territorial stability. Allowing political rivalry or strategic competition to erode this rule would undermine the Charter framework. For that reason, the threshold for lawful deviation remains deliberately high.

Accordingly, the starting point for analysing the USA-Iran War is clear. Cross-border military strikes directed at the territory of another State fall within the scope of Article 2(4). They are presumed unlawful unless justified by Security Council authorisation, valid consent, or the strict requirements of self-defence. The subsequent sections examine whether such a justification can be sustained under Article 51.

4. Self-Defence under Article 51

Article 51 of the United Nations Charter recognises the inherent right of individual or collective self-defence if an armed attack occurs against a Member State (United Nations, 1945). This provision constitutes the principal exception to the prohibition of force in Article 2(4). In the context of the USA-Iran War, both sides framed aspects of their conduct as defensive. The legality of those claims depends on strict compliance with the established conditions of self-defence.

International jurisprudence and State practice require that five elements be satisfied: the existence of an armed attack, attribution of that attack to a State, necessity, proportionality, and reporting to the Security Council (ICJ, 1986; ICJ, 2003; Gray, 2018). These conditions are cumulative. Failure to satisfy any one of them undermines the legality of the claim.

4.1 Armed Attack Threshold

The first requirement is the existence of an armed attack. The International Court of Justice has clarified that not every use of force qualifies as an armed attack. Only the “most grave forms of the use of force” reach that threshold (ICJ, 1986). Minor frontier incidents, isolated skirmishes, or limited exchanges may constitute unlawful uses of force but do not automatically trigger the right of self-defence.

In the 2026 escalation, the initial large-scale strikes were conducted under Operation Epic Fury and Operation Roaring Lion. The decisive question is whether, prior to 28 February 2026, Iran had carried out a grave armed attack against the United States or Israel. Large-scale missile or drone strikes causing substantial destruction or casualties would meet the gravity standard. By contrast, low-intensity incidents or indirect hostile acts would not.

The threshold analysis requires an objective assessment of scale and effects. The existence of political hostility or long-term strategic rivalry is legally irrelevant. The inquiry focuses on whether a grave armed attack occurred in fact.

4.2 Attribution to the State

Even if an armed attack occurred, it must be attributable to a State. Where regular armed forces conduct the attack, attribution is straightforward. More complex issues arise if proxy groups or non-State actors are involved.

The ICJ in Nicaragua required “effective control” over specific operations for conduct of non-State actors to be attributable to a State (ICJ, 1986). General support, financing or ideological alignment is insufficient. The International Law Commission’s Articles on State Responsibility similarly require that the conduct be carried out by State organs or persons acting under State instructions or control (ILC, 2001).

In the USA-Iran War, if attacks preceding 28 February were carried out by affiliated armed groups, the legal assessment depends on whether the required degree of operational control can be established. The evidentiary burden lies with the State invoking self-defence. Without attribution, defensive force directed against the territory of another State lacks a lawful basis.

4.3 Necessity

Self-defence must be necessary. Necessity requires that force be the only reasonable means available to halt or repel the armed attack. Diplomatic engagement, recourse to the Security Council, or other peaceful measures must be considered before force is used (Dinstein, 2017).

In assessing necessity in the USA-Iran War, the timing and circumstances of the February 28 strikes are relevant. If no armed attack was ongoing or imminent in the strict legal sense, the requirement of necessity is difficult to satisfy. Preventive action based on general security concerns does not meet the orthodox standard reflected in jurisprudence and State practice (Gray, 2018).

Necessity also has a temporal dimension. Defensive force must respond to an armed attack that is ongoing or imminent. Force employed long after the alleged attack, or in circumstances where the threat has dissipated, does not meet the requirement.

4.4 Proportionality

Proportionality limits the scale and scope of defensive force. The objective of self-defence is to halt and repel the armed attack, not to punish the attacker or pursue broader strategic aims. The International Court of Justice has emphasised that defensive measures must be proportionate to the attack suffered (ICJ, 2003).

In practical terms, proportionality requires comparison between the gravity of the armed attack and the intensity, duration, and geographic scope of the response. Large-scale bombardment extending beyond immediate military objectives may exceed what is necessary to repel the attack. Proportionality does not demand symmetry in weapons or casualties, but it requires that the response remain confined to defensive purposes.

In the context of the USA-Iran War, the breadth of Operation Epic Fury and Operation Roaring Lion must be measured against the specific armed attack allegedly being addressed. If the response pursued broader strategic objectives unrelated to stopping an ongoing attack, it may fall outside lawful self-defence.

4.5 Reporting Obligation

Article 51 requires that measures taken in self-defence be immediately reported to the Security Council (United Nations, 1945). This obligation reinforces the collective security framework and allows the Council to assume responsibility for maintaining international peace and security.

Failure to report does not automatically render a use of force unlawful, but it weakens the credibility of the self-defence claim. Prompt reporting signals that the acting State recognises the exceptional nature of its conduct and remains within the Charter framework (Gray, 2018).

In the USA-Iran War, compliance with the reporting requirement forms part of the overall legality assessment. The content and timing of any communications to the Security Council provide insight into how the acting States legally characterised their conduct.

Self-defence under Article 51 is not a flexible political doctrine. It is a narrowly framed legal exception to a fundamental prohibition. In the 2026 USA-Iran War, the legality of defensive claims depends on strict satisfaction of the armed attack threshold, attribution, necessity, proportionality, and reporting requirements. These elements provide the structured framework through which the lawfulness of the resort to force must be assessed.

5. Anticipatory and Preventive Self-Defence Claims

The current war also raises the question of whether the initial resort to force was justified based on an imminent threat rather than a completed armed attack. Some official statements surrounding Operation Epic Fury and Operation Roaring Lion referred to urgent security risks and the need to neutralise emerging dangers. Such language implicates the doctrine of anticipatory self-defence.

Article 51 of the United Nations Charter recognises self-defence “if an armed attack occurs” (United Nations, 1945). The text does not expressly mention anticipatory action. Nonetheless, some States and scholars argue that self-defence may be exercised in response to an imminent armed attack, provided that the threat is immediate and overwhelming. This position draws upon the nineteenth-century Caroline correspondence, which formulated a standard of necessity that must be “instant, overwhelming, leaving no choice of means, and no moment for deliberation” (Moore, 1906).

Modern jurisprudence has not unequivocally endorsed a broad right of anticipatory self-defence. The International Court of Justice has consistently focused on the occurrence of an armed attack and has avoided expanding the doctrine to encompass preventive force based on generalised future risks (ICJ, 1986; ICJ, 2003). The prevailing interpretation in contemporary doctrine treats anticipatory self-defence as lawful only where the armed attack is imminent in a strict temporal and factual sense (Gray, 2018).

In assessing the USA-Iran War, the key issue is whether the February 28 strikes responded to a specific and imminent armed attack, or whether they were based on broader assessments of long-term strategic danger. An imminent threat requires credible and concrete evidence that an armed attack was about to occur. Preparatory measures, military build-up, or capability development alone do not automatically satisfy this requirement. The legal test concerns immediacy and inevitability, not potential or capacity.

Preventive war differs fundamentally from anticipatory self-defence. Preventive force is directed at neutralising a possible future threat that is neither imminent nor operationally underway. Contemporary international law does not recognise preventive war as lawful under Article 51 (Corten, 2020). Accepting such a doctrine would significantly erode the prohibition of force by allowing States to act unilaterally on speculative risk assessments.

In the context of the USA-Iran War, if the initial strikes were justified primarily by reference to long-term concerns regarding military capability or regional influence, rather than a demonstrably imminent armed attack, the claim would more closely resemble preventive force. The legality of anticipatory self-defence depends on strict evidence of immediacy. The broader and more strategic the stated objectives, the more difficult it becomes to characterise the action as anticipatory rather than preventive.

The distinction between imminence and prevention is therefore central. Lawful anticipatory self-defence requires a narrowly defined and temporally immediate threat. Preventive war rests on strategic calculations about future risk and is not supported by the Charter framework. The assessment of the USA-Iran War must determine on which side of this line the February 28 operations fall.

6. Non-State Actors and Proxy Warfare

The USA-Iran War unfolded in a regional environment characterised by the presence of armed non-State actors operating across borders. Militia groups aligned with broader geopolitical blocs have long been active in the Middle East. In assessing the legality of force in 2026, it is therefore necessary to determine whether attacks carried out by affiliated militias could trigger the right of self-defence under Article 51 of the UN Charter.

International law recognises that an armed attack may originate from non-State actors. The central issue is attribution. If the attack is legally attributable to a State, self-defence may be exercised against that State. The International Court of Justice in Nicaragua required “effective control” over the specific operation for conduct of non-State actors to be attributed to a State (ICJ, 1986). General support, financing, or political alignment is insufficient. The International Law Commission’s Articles on State Responsibility reflect the same structure: attribution requires that the actors operate under the instructions, direction, or control of the State in relation to the specific conduct (ILC, 2001).

In the context of the USA-Iran War, if missile or drone attacks against U.S. or Israeli targets were carried out by militias affiliated with Iran, the legality of direct strikes against Iranian territory depends on whether those militia actions can be legally imputed to Iran. The evidentiary burden lies with the State invoking self-defence. Without proof of the requisite degree of control, force directed against the territorial State may exceed the lawful scope of Article 51.

A separate and contested issue concerns the so-called “unable or unwilling” doctrine. Some States have argued that when a non-State actor launches armed attacks from the territory of another State, and that territorial State is unable or unwilling to prevent such attacks, the victim State may use force within that territory in self-defence. This position has appeared in certain State practice, particularly in counter-terrorism contexts. However, it remains controversial and has not been clearly endorsed by the International Court of Justice (Gray, 2018; Corten, 2020).

The orthodox interpretation of Article 51 does not expressly incorporate the “unable or unwilling” test. Instead, it emphasises the occurrence of an armed attack and its attribution. Expanding self-defence to include unilateral determinations of another State’s inability or unwillingness risks diluting the prohibition of force and undermining the principle of sovereignty. For that reason, many scholars and States maintain that cross-border force against non-State actors located within another State’s territory is lawful only if the attack is attributable to that State or if that State consents to the operation.

In evaluating the USA-Iran War, two distinct legal questions arise. First, did attacks by affiliated militias meet the gravity threshold of an armed attack? Second, can those attacks be legally attributed to Iran under accepted standards of control? If attribution is not established, reliance on the “unable or unwilling” doctrine would represent a broader and more contested interpretation of Article 51.

Proxy warfare complicates legal classification but does not suspend the Charter framework. The right of self-defence is triggered by legally defined armed attacks, not by general patterns of hostility or indirect rivalry. In the 2026 conflict, careful separation between political alignment and legal control is essential. Only where the requirements of attribution and gravity are satisfied can militia activity serve as a lawful basis for cross-border self-defence under contemporary international law.

7. Security Council and Collective Security Failure

The USA-Iran War must also be examined within the framework of collective security established by the United Nations Charter. Under Chapter VII, the Security Council holds primary responsibility for the maintenance of international peace and security (United Nations, 1945). The Council may determine the existence of a threat to the peace, breach of the peace, or act of aggression and may authorise the use of force to restore international stability.

In the 2026 escalation, no Security Council resolution authorised the initial cross-border strikes conducted under Operation Epic Fury and Operation Roaring Lion. The absence of express authorisation is legally significant. Under the Charter system, unilateral resort to force is lawful only in self-defence or with Security Council approval. Without such approval, the legality of military action depends exclusively on Article 51.

Following the outbreak of hostilities, the Council convened to address the situation. However, divergent geopolitical positions among permanent members prevented the adoption of a binding resolution authorising force or imposing collective enforcement measures. The veto power embedded in Article 27 of the Charter allows any permanent member to block substantive decisions. Where major powers are directly or indirectly involved in a conflict, institutional deadlock is a recurrent structural feature of the Council’s operation (Gray, 2018).

This paralysis does not alter the legal framework governing the use of force. The Charter does not provide that failure of the Security Council to act expands the unilateral rights of States. The absence of collective action does not create a residual entitlement to resort to force beyond the strict confines of self-defence. The International Court of Justice has consistently interpreted the Charter as maintaining a clear distinction between collective enforcement under Chapter VII and unilateral action under Article 51 (ICJ, 1986).

Some States have argued in past crises that Council inaction justifies alternative mechanisms, including regional arrangements or broader interpretations of self-defence. Such arguments remain controversial and are not supported by the text of the Charter. The collective security system may be politically constrained, but its structural limits do not modify the substantive prohibition in Article 2(4).

The 2026 conflict illustrates a recurring tension within the Charter system. When permanent members are directly implicated in hostilities, the Council’s capacity to act decisively is limited. This institutional reality may weaken enforcement, but it does not transform the legal standards governing force. The prohibition of force and the conditions of self-defence remain applicable irrespective of Council effectiveness.

The Security Council’s debates and any formal communications submitted under Article 51 form part of the legal record. However, Council paralysis does not confer legitimacy on unilateral uses of force. The legality of actions in the USA-Iran War must therefore be assessed under the established jus ad bellum framework, independent of the Council’s political dynamics.

8. Consent and Intervention by Invitation

This war also engaged questions of consent where military operations were conducted from or within the territory of third States. Under international law, the prohibition in Article 2(4) of the UN Charter protects the territorial integrity of States. However, if a territorial State validly consents to the presence or use of force by another State on its territory, the sovereignty element of Article 2(4) is not violated (Crawford, 2019).

Consent must satisfy strict legal conditions. It must be given by a competent authority representing the State, be clearly expressed, and not be the product of coercion. Consent may be limited in scope, duration, or purpose. Military action that exceeds the scope of consent may constitute a separate violation of sovereignty.

In the 2026 hostilities, if U.S. or Israeli operations were launched from military bases located in neighbouring States, the legality of those operations depends in part on whether those States provided valid consent. Such consent does not legalise strikes directed against Iran unless the substantive requirements of self-defence or Security Council authorisation are independently satisfied. Consent operates to remove the violation of the territorial State’s sovereignty, but does not provide an autonomous basis for using force against a third State.

Consent may also arise in the context of collective self-defence. If a State that has suffered an armed attack formally requests assistance, supporting States may lawfully use force on its behalf under Article 51 (United Nations, 1945). The existence of a clear and explicit request is essential. Without it, collective defensive action lacks a valid foundation (ICJ, 1986).

Accordingly, in the USA-Iran War, any reliance on intervention by invitation requires careful examination of the identity of the consenting authority, the clarity of the consent, and the limits placed upon it. Consent cannot serve as a substitute for the Charter requirements governing the use of force against another sovereign State.

9. Reprisals and Retaliatory Force

Armed reprisals are prohibited under contemporary international law. Following the adoption of the UN Charter, the use of force as retaliation for a prior unlawful act is not permitted unless it satisfies the strict requirements of self-defence under Article 51 (Brownlie, 1963; Gray, 2018). The Charter framework replaced earlier doctrines that tolerated forcible reprisals.

A reprisal involves the use of force in response to a prior wrongful act with the purpose of punishment or coercion. Such measures are distinct from self-defence, which is limited to halting or repelling an armed attack. The International Court of Justice has affirmed that armed reprisals in peacetime are unlawful (ICJ, 1986).

In the 2026 conflict, several public statements characterised subsequent operations as “retaliation.” The legal significance of this terminology depends on substance rather than language. If force was used solely to punish prior conduct or to deter future behaviour unrelated to an ongoing armed attack, it would fall outside the scope of lawful self-defence. Defensive action must be necessary and proportionate to stopping an armed attack. It cannot lawfully pursue punitive objectives.

Therefore, any operation within the USA-Iran War described as retaliatory must be assessed against Article 51 criteria. If the action responded to a grave armed attack and satisfied necessity and proportionality, it may qualify as self-defence. If it exceeded those limits or was undertaken after the cessation of hostilities without defensive justification, it would constitute an unlawful reprisal.

The prohibition of armed reprisals reinforces the stability of the Charter system. Allowing States to respond to alleged wrongs with punitive force would undermine the general prohibition in Article 2(4). The legality of actions during the USA-Iran War must therefore be determined through the structured framework of self-defence, not through political characterisations of retaliation.

10. Maritime Operations and the Law of Naval Warfare

The war unfolded partly in a maritime theatre, particularly in and around the Persian Gulf. Naval deployments, reported attacks on military vessels, and risks to commercial shipping raised legal issues under both jus ad bellum and the law governing naval warfare.

Under jus ad bellum, an attack on a warship is widely recognised as capable of constituting an armed attack within the meaning of Article 51 of the UN Charter, depending on its scale and consequences (Dinstein, 2017). If naval vessels of either party were struck by missiles, drones, or mines, causing significant destruction or casualties, such incidents could independently trigger the right of self-defence. The legal assessment would follow the same structure applied on land: armed attack, attribution, necessity, and proportionality.

Interference with commercial shipping presents additional concerns. Merchant vessels enjoy protection under peacetime law of the sea, including freedom of navigation principles reflected in the United Nations Convention on the Law of the Sea (UNCLOS). During an international armed conflict, belligerent rights at sea are governed by customary naval warfare rules, including those reflected in the San Remo Manual (1994). Commercial vessels may not be targeted unless they become military objectives. Indiscriminate attacks on civilian shipping would violate both the prohibition of force and international humanitarian law.

Blockades constitute another relevant issue. A naval blockade may be lawful in an international armed conflict if it is declared, effective, non-discriminatory, and directed at legitimate military objectives. However, blockades must comply with humanitarian limits, including the prohibition on starvation of civilians as a method of warfare and the obligation to allow passage of essential supplies (International Committee of the Red Cross, 2020). A blockade imposed outside an armed conflict, or without meeting effectiveness requirements, may constitute an unlawful use of force.

Strikes on offshore infrastructure, including oil platforms or maritime installations, also require careful classification. In Oil Platforms, the International Court of Justice assessed whether the destruction of Iranian platforms was justified as self-defence and examined whether the targets qualified as legitimate military objectives (ICJ, 2003). The Court required proof of both jus ad bellum justification and compliance with targeting rules. In the 2026 context, any attacks on offshore facilities must satisfy the same dual test: lawful resort to force and lawful conduct of hostilities.

Maritime operations in the Iran War, therefore, engage layered legal analysis. The initial resort to force must comply with Article 2(4) and Article 51. Once an international armed conflict exists, naval operations must further comply with the principles of distinction, proportionality, and precautions in attack under international humanitarian law.

11. Cyber Operations

The 2026 hostilities reportedly included cyber operations alongside kinetic strikes. International law does not treat cyber activities as legally exceptional. Their classification depends on scale and effects.

A cyber operation may constitute a “use of force” if its consequences are comparable to those produced by kinetic military action. Destruction of infrastructure, disabling of air defence systems, causing physical damage, or operations resulting in casualties may reach this threshold (Schmitt, 2017). If the effects are sufficiently grave, such operations could qualify as an “armed attack,” thereby potentially triggering self-defence rights.

By contrast, cyber espionage, data theft, or temporary service disruption without physical damage generally fall below the use-of-force threshold. Such activities may be unlawful under other legal regimes, but do not automatically justify kinetic response.

Attribution presents particular challenges in cyberspace. Establishing that a cyber operation is attributable to a State requires reliable technical and intelligence evidence. Under the law of State responsibility, the effective control standard remains relevant where non-State actors conduct cyber attacks (International Law Commission, 2001). Absent clear attribution, reliance on self-defence against a territorial State becomes legally problematic.

Proportionality also applies in the cyber domain. A State responding to a cyber operation must ensure that its defensive measures are necessary to halt the attack and proportionate to its scale and effects. A large-scale kinetic strike in response to limited cyber disruption may fail the proportionality test.

In the USA-Iran War, the legality of cyber components depends on whether their scale and consequences crossed the use-of-force threshold and whether attribution to a State can be established under accepted standards.

12. Jus in Bello Implications

Once a reciprocal large-scale force occurred between regular armed forces, the USA-Iran War qualified as an international armed conflict under Common Article 2 of the 1949 Geneva Conventions (United Nations, 1949). From that point onward, international humanitarian law governed the conduct of hostilities.

The principle of distinction requires parties to direct operations only against military objectives and to distinguish at all times between civilians and combatants. Attacks against civilian populations or civilian objects are prohibited. Military objectives are limited to objects that by their nature, location, purpose, or use make an effective contribution to military action and whose destruction offers a definite military advantage (International Committee of the Red Cross, 2020).

Proportionality in targeting prohibits attacks expected to cause excessive incidental civilian harm in relation to the concrete and direct military advantage anticipated. This rule applies independently of jus ad bellum considerations. Even if a resort to force were lawful under Article 51, individual strikes must comply with humanitarian proportionality standards.

The obligation to take precautions in attack further requires feasible measures to verify targets, choose means and methods of warfare that minimise civilian harm, and provide effective warnings where circumstances permit. These duties apply equally to aerial bombardment, missile strikes, and naval operations.

Treatment of captured personnel is governed by the Third Geneva Convention. Prisoners of war must be protected against violence, intimidation, and public curiosity, and must receive humane treatment at all times. Civilians detained in connection with the conflict are protected under the Fourth Geneva Convention.

Compliance with jus in bello does not retroactively validate an unlawful resort to force. The two legal regimes operate independently. However, once an international armed conflict exists, both parties are bound by humanitarian law regardless of which side initiated hostilities.

The maritime and cyber dimensions of the USA-Iran War do not displace these humanitarian obligations. Naval engagements must respect targeting and neutrality rules. Cyber operations integrated into kinetic attacks must also comply with distinction and proportionality principles if they produce effects within the armed conflict.

The 2026 war, therefore, requires dual legal scrutiny. Jus ad bellum governs the legality of resort to force. Jus in bello governs the legality of conduct during hostilities. Both frameworks apply concurrently once the threshold of international armed conflict has been crossed.

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13. State Responsibility and Reparations

If violations of the prohibition of force or of international humanitarian law occurred during the hostilities, the legal consequences are governed by the law of State responsibility. Under customary international law, as reflected in the Articles on Responsibility of States for Internationally Wrongful Acts, an internationally wrongful act entails responsibility and triggers specific legal obligations (International Law Commission, 2001).

The first consequence is cessation. A State responsible for an ongoing wrongful act must cease that conduct immediately. In the context of unlawful uses of force, this obligation requires termination of the offending military operations. Cessation is forward-looking and aims at restoring compliance with international law.

The second consequence is the obligation of non-repetition. Where circumstances indicate a risk of recurring violations, the responsible State may be required to provide assurances and guarantees that similar conduct will not be repeated. This requirement is particularly relevant in cases involving unlawful resort to force or systematic violations of humanitarian law.

The third consequence is reparation. Reparation must, as far as possible, wipe out the consequences of the wrongful act (Permanent Court of International Justice, 1928). Reparation may take the form of restitution, compensation, or satisfaction. Restitution seeks to re-establish the situation that existed before the wrongful act. Where restitution is materially impossible, compensation for financially assessable damage is required. Satisfaction may involve a formal acknowledgment of the breach or an apology.

In the 2026 conflict, if the initial resort to force were found inconsistent with Article 2(4) of the UN Charter, the responsible State would incur responsibility for the resulting injury. Similarly, serious violations of international humanitarian law, such as unlawful targeting of civilians, would generate separate obligations of reparation.

Dispute settlement mechanisms may be engaged. The International Court of Justice has jurisdiction where States have accepted it through compromissory clauses, optional clause declarations, or special agreements. In the absence of consent to jurisdiction, proceedings before the Court cannot be imposed unilaterally. Arbitration constitutes an alternative avenue where both parties agree to submit specific disputes to a binding determination. Historical precedent demonstrates that even politically charged disputes may eventually be resolved through negotiated settlements or claims mechanisms rather than immediate judicial adjudication.

State responsibility operates independently of individual criminal responsibility. It concerns the legal accountability of the State as an entity, not the personal culpability of decision-makers. The existence of armed conflict does not displace these obligations. Even in wartime, breaches of international law entail responsibility and corresponding remedial duties.

14. Individual Criminal Responsibility

Separate from State responsibility is the question of individual criminal responsibility. International law recognises that certain grave violations entail personal liability for political leaders, military commanders, and other individuals. The most relevant categories in the context of the 2026 hostilities are the crime of aggression and war crimes.

The crime of aggression, as codified in Article 8 bis of the Rome Statute of the International Criminal Court (ICC), concerns the planning, preparation, initiation, or execution of an act of aggression by a person in a leadership position (International Criminal Court, 1998). An act of aggression is defined as the use of armed force by a State against the sovereignty, territorial integrity, or political independence of another State in a manner inconsistent with the UN Charter. However, the ICC’s jurisdiction over the crime of aggression is subject to strict limitations. It applies only to States Parties that have ratified the relevant amendments, and jurisdiction may be restricted where the alleged aggressor State is not bound by those provisions.

War crimes involve serious violations of international humanitarian law committed in the context of an international armed conflict. These include intentionally directing attacks against civilians, disproportionate attacks causing excessive civilian harm, mistreatment of prisoners of war, and targeting of protected objects. Jurisdiction over war crimes may arise before the ICC where territorial or nationality conditions are satisfied, or before domestic courts exercising universal jurisdiction in accordance with national legislation.

Jurisdictional constraints are central. The ICC may exercise jurisdiction only where the alleged crimes were committed on the territory of a State Party, by a national of a State Party, or where jurisdiction has been accepted by the State concerned. Alternatively, the Security Council may refer a situation to the Court under Chapter VII of the UN Charter. In politically sensitive conflicts involving major powers, such referrals may face veto obstacles.

Domestic courts may also prosecute individuals for war crimes or aggression under national law, particularly where universal jurisdiction statutes apply. The principle that certain crimes affect the international community as a whole supports such proceedings.

Individual criminal responsibility does not depend on a prior finding of State responsibility. A military operation that violates jus ad bellum does not automatically constitute a war crime, and conversely, a conflict initiated unlawfully may still involve compliance with humanitarian law in specific operations. The two regimes remain distinct but complementary.

The hostilities, therefore, engage a dual accountability structure. States may incur responsibility for internationally wrongful acts requiring cessation and reparation. Individuals may incur criminal liability where conduct satisfies the elements of aggression or war crimes and jurisdictional conditions are met.

15. Conclusion

The legal evaluation of the hostilities must return to the first principles of the United Nations Charter. The initial resort to force on 28 February 2026 consisted of coordinated cross-border strikes by the United States and Israel against Iranian territory. Under Article 2(4) of the Charter, such action is prima facie unlawful unless justified by Security Council authorisation, valid consent, or self-defence (United Nations, 1945). No Security Council authorisation preceded the strikes. The legality of the initial action, therefore, depends entirely on whether the strict conditions of Article 51 were satisfied.

For self-defence to apply, a prior armed attack of sufficient gravity must have occurred. The jurisprudence of the International Court of Justice requires that only the “most grave forms” of force trigger that right (ICJ, 1986). If no such armed attack preceded the February 28 operations, the initial resort to force cannot be justified under orthodox doctrine. Claims based on broader strategic threats or long-term capability concerns fall closer to preventive force than to lawful self-defence, and preventive war is not recognised as lawful under the Charter framework (Gray, 2018; Corten, 2020).

Subsequent Iranian retaliatory strikes must be assessed independently. Once reciprocal missile and aerial operations occurred, the situation constituted an international armed conflict under international humanitarian law (United Nations, 1949). From that point forward, both sides were bound by the principles of distinction, proportionality, and precautions in attack. Even if one party’s initial resort to force were unlawful, the other party’s response remains constrained by the requirements of necessity and proportionality under Article 51. Defensive force may halt or repel an armed attack but may not lawfully evolve into punitive or strategic escalation beyond that objective (ICJ, 2003).

The conflict also exposed structural limitations within the collective security system. The Security Council did not authorise the use of force and was unable to adopt binding measures due to geopolitical divisions. However, Council paralysis does not expand unilateral rights to use force. The Charter does not recognise institutional deadlock as a substitute for the strict conditions of self-defence. The prohibition of force remains operative irrespective of political constraints within the Council (United Nations, 1945).

From a systemic perspective, the 2026 hostilities illustrate both the resilience and fragility of the Charter order. The resilience lies in the continued relevance of clear legal standards: armed attack, attribution, necessity, proportionality, and reporting. These criteria provide a structured framework for assessing legality even in high-intensity conflict. The fragility lies in the political realities that may tempt States to interpret those standards expansively when facing strategic rivalry.

The 2026 USA-Iran War demonstrates that the prohibition of force remains the foundational rule, and that exceptions must be interpreted narrowly. Where anticipatory or preventive doctrines expand beyond imminence and objective necessity, the Charter’s integrity is placed at risk. Where defensive action remains confined to halting a grave armed attack and complies with humanitarian constraints, the legal order retains coherence.

The enduring lesson of the 2026 conflict is that international law does not disappear during crises. It continues to regulate both the decision to use force and the manner in which force is employed. Whether the events of 2026 ultimately strengthen or weaken the Charter system depends less on rhetoric and more on consistent adherence to its core principles.

References

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