Beyond its immediate destabilising effects on the Middle East’s balance of power, the February 2026 U.S.-Israel war on Iran has resurrected a contested and consequential debate: the interpretation of foundational norms in international law.
Although this intervention was initially justified as ‘security’ and ‘threat’, closer analysis reveals significant strain between the prohibition on force and the right to self-defence. These developments heighten concerns that exceptional mechanisms in international law are being gradually expanded, undermining its core principles.
Within this framework, it is crucial to assess the conflict by examining both the military actions taken by the belligerent states and the legal grounds they cite to justify those actions. The core issue is not only the legitimacy of any single operation but also the ongoing viability of the international system’s legal principles that are designed to restrict the use of force. In this context, analysing the interventions by the United States and Israel, along with Iran’s response, provides a concrete example to reassess how international law governs armed conflict.
This paper argues that the Iran war reflects not merely a violation of existing norms, but a broader shift in the interpretive practice of international law, whereby the doctrine of self-defence is increasingly invoked to legitimise preventive uses of force. This evolution risks transforming an exception designed to preserve the legal order into a mechanism that gradually erodes it from within.
The Prohibition of the Use of Force
It must be asserted from the outset that the military operations conducted by the United States and Israel against Iran constitute a clear breach of one of the most fundamental and peremptory norms of international law: the prohibition of the use of force. This prohibition is not merely enshrined with absolute clarity in Article 2(4) of the UN Charter; it is also an integral part of customary international law and possesses the status of jus cogens. Therefore, a violation of this rule represents a grave illegality that undermines the very foundations of the international legal order.
Historically, until the First World War, war was seen as a natural extension of sovereign power and a tool of foreign policy. Under the doctrine of ‘just cause’, states used force to protect their interests. However, the devastation of the Great War led to a profound reassessment. Initiatives like the Kellogg-Briand Pact aimed —to limit recourse to war. Yet, it took the catastrophe of the Second World War to bring lasting normative change.
The 1945 UN Charter categorically prohibited not only force but also threats of force in international relations. This shift marked the transition from the ‘law of might’ to the ‘rule of law.’ Article 2(4) states:
“All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.”
There are only two exceptions to this general prohibition. These are: (i) authorisation by the UN Security Council to maintain or restore international peace and security, and (ii) the exercise of the inherent right of self-defence. In this case, it is clear that no Security Council resolution authorises the use of force against Iran. The legal crux of the debate is whether this intervention can be justified as self-defence.
The Right of Self-Defence in International Law
While the prohibition on the use of force is absolute, states retain the right to self-defence. Article 51 of the UN Charter establishes this balance:
“Nothing in the present Charter shall impair the inherent right of individual or collective self-defence if an armed attack occurs against a Member of the United Nations…”
The US and Israel base their operations on the claim of collective self-defence. The legal validity of this depends on examining whether the required conditions for self-defence have been met.
First, an ‘armed attack’ is required. UN General Assembly Resolution 3314 (1974) defines such acts as invasion, bombardment, or blockade. In this scenario, there is no evidence that Iran initiated such an attack against the US or Israel. Instead, the conflict began with operations launched by the US and Israel.
At this stage, we must distinguish between ‘anticipatory’ and ‘pre-emptive’ self-defence. The doctrine of anticipatory self-defence is accepted in international law and is based on the 1837 Caroline Case. The use of force is lawful when the necessity of self-defence is ‘instant, overwhelming, leaving no choice of means, and no moment for deliberation’. The threat in this context must be imminent. A state does not have to wait for an attack if it faces a certain and immediate threat. To wait could be ‘strategic suicide’.
In contrast, ‘pre-emptive’ self-defence seeks to justify the use of force based on future, non-imminent threats. This approach is widely rejected by international law. It could render the prohibition on the use of force meaningless by allowing arbitrary interventions based on subjective perceptions of security.
In this framework, the United States and Israeli intervention is not based on an imminent threat from Iran. Rather, it relies on Iran’s alleged capabilities and perceived potential threat. Without a ‘clear and present’ threat meeting the Caroline criteria, this action exceeds lawful self-defence and is an example of pre-emptive force.
One can play the devil’s advocate and argue that contemporary threat environments, particularly those involving proxy actors, missile capabilities, and latent nuclear potential, challenge the traditional threshold of imminence. Proponents of a broader interpretation of self-defence contend that waiting for a fully materialised attack may no longer be viable in such contexts. Yet, accepting such reasoning without strict evidentiary standards risks collapsing the distinction between anticipatory and preventive force altogether, thereby undermining the very constraint the Caroline doctrine was intended to preserve.
The justification for the nuclear threat has many inconsistencies. US and Israeli officials, in June 2025, called previous strikes a ‘victory’ that largely neutralised Iran’s nuclear capabilities. Invoking the same threat now, without verifiable evidence that Iran rebuilt its capacity, seems political rather than a valid legal justification.
Even if Iran had nuclear weapons, this would not justify force. The International Court of Justice’s 1996 Advisory Opinion stated that merely possessing such capacity does not constitute an illegal ‘threat’ under international law. Claiming self-defence based on an unproven capacity violates the UN Charter and legal interpretation. Coupled with no proof of intent to weaponise—and with religious decrees outlawing such weapons—the use of force appears as a political transgression, not a legal necessity.
The operations against Iran by the United States and Israel lack both UN Security Council authorisation and the requirements of self-defence. The intervention should be seen as a violation of the prohibition of the use of force and as an act of aggression without legal basis.
Iran as the True Bearer of the Right to Self-Defence
Describing the US and Israeli operations against Iran as unlawful acts leads to a key legal question. How should Iran’s response be assessed under international law? It is crucial to examine Iran’s counter-attacks—against both Israeli military targets and US assets, especially bases in Gulf states—are legitimate acts of self-defence.
As the International Court of Justice (ICJ) explicitly established in the case of Nicaragua v. United States (1986), the direct use of military force by one state against another is recognised as an act that crosses the threshold of an ‘armed attack’. Within this framework, there is little legal doubt that the military operations by the US and Israel against Iran meet this threshold, thereby triggering Iran’s inherent right to self-defence. However, this finding does not imply that the right to self-defence may be exercised without limit; on the contrary, the scope and manner of this right are strictly circumscribed by established principles of international law.
At this juncture, the principle of distinction, a cornerstone of International Humanitarian Law (IHL), is decisive. In IHL, the question of ‘who or what may be targeted’ is answered through the concept of a legitimate military objective. The most definitive and universal definition of this concept is found in Article 52(2) of Additional Protocol I (1977). According to this, for an object to be classified as a military objective, two conditions must be met cumulatively: (i) the object must, by its nature, location, purpose, or use, make an effective contribution to military action, and (ii) its total or partial destruction must offer a definite military advantage.
Evaluated in this light, US and Israeli military assets that played a direct role in the strikes against Iran—or form part of that offensive capacity, such as US naval forces, aircraft carriers, and Israeli military installations—clearly constitute legitimate military objectives for Iran. Thus, strikes against such targets can, in principle, be considered within the lawful exercise of the right to self-defence.
Nevertheless, the exercise of self-defence is strictly limited by the principles of necessity and proportionality. These principles are both an inseparable part of customary international law and established judicial criteria, as reaffirmed by the ICJ in the Oil Platforms (2003) case. Accordingly, each counterattack by Iran must be assessed on a case-by-case basis to determine whether it was necessary to repel the attack and whether the force used was proportionate to the initial strike.
Targeting Military Bases on the Territory of Third States
The legal status of Iran targeting US military bases stationed within Gulf countries represents the most controversial dimension of the issue. According to the classical approach to international law, the right to self-defence may only be exercised against the state that launched the armed attack; the territorial integrity of third states is, as a rule, sacrosanct. However, contemporary state practice and doctrine have developed more nuanced interpretations that relax this rigid approach under certain circumstances.
Particularly in the post-9/11 era, the ‘unwilling or unable’ doctrine has gained prominence. This approach posits that if a state is either unwilling or unable to prevent its territory from being used for armed attacks against another state, the victim state may use limited force against the threat elements located on that territory. While the status of this doctrine within customary international law remains a subject of intense debate, its significance in international practice cannot be denied.
Furthermore, a similar conclusion can be reached through a more established legal grounding. It is generally accepted that if a state permits a foreign military power to be stationed on its territory, and that power subsequently launches an armed attack against another state, those specific military facilities may become legitimate military objectives. This approach is directly consistent with the definition of a military objective under International Humanitarian Law.
In this context, if United States military bases in Gulf countries were in fact used in operations against Iran, targeting these bases would clearly fall within the scope of self-defence. From a broader perspective, even if these bases were not directly involved in the strike, they could be considered ‘ready and constant military infrastructure posing an ongoing threat’ and thus part of the offensive capacity directed at Iran. Under these specific conditions, Iran’s targeting of such facilities could therefore be interpreted as consistent with the right to self-defence.
Nevertheless, this interpretation remains legally contentious and must be approached with caution. Expanding the category of legitimate targets to include broadly defined ‘potential threats’ risks replicating the same expansive logic of self-defence that underpins the initial use of force. Without a strict, evidence-based application of necessity and proportionality, such reasoning may contribute to a broader erosion of the legal limits governing the use of force.
Conversely, should Iran’s counter-attacks target the civilian infrastructure of third states or economic objectives that do not directly contribute to military action, such as civilian energy facilities, this would constitute a manifest violation of International Humanitarian Law. Such facilities can only acquire the status of a legitimate target insofar as they serve direct military purposes. Otherwise, such strikes would violate both the principle of distinction and the principle of proportionality, thereby constituting unlawful acts that exceed the boundaries of the right to self-defence.
The Status of the Strait of Hormuz
The legal nature of Iran’s measures to restrict vessel passage through the Strait of Hormuz, in the context of the armed conflict with the US and Israel, presents a complex issue situated at the intersection of international law of the sea and the law on the use of force (jus ad bellum). To address this, one must first delineate the Strait’s legal status and the applicable passage regime.
By virtue of its geographical and functional characteristics, the Strait of Hormuz constitutes an ‘international strait’, connecting high seas or exclusive economic zones and serving as a vital artery for international maritime navigation. Under the 1982 United Nations Convention on the Law of the Sea (UNCLOS), the regime applicable to such straits is that of ‘transit passage’. Set out in Part III of UNCLOS, this regime grants all ships and aircraft the right of passage, provided it is ‘continuous and expeditious’. Crucially, coastal states are prohibited from arbitrarily suspending this passage.
However, two significant caveats complicate this general framework. Firstly, the applicability of this regime depends on whether the relevant states are parties to UNCLOS. Iran is not a party to the Convention and does not recognise the transit passage regime as binding upon itself. Secondly, while it is debated whether transit passage has attained the status of customary international law, Iran’s long-standing, overt, and consistent objections place it in the position of a ‘persistent objector’. According to the classic doctrine on the formation of customary law, this status renders the rule’s binding force highly questionable in Iran.
Within this context, Iran’s reliance on a more restrictive passage regime—akin to the ‘innocent passage’ model—and its imposition of limitations on certain vessels cannot be dismissed as an entirely baseless claim from a purely maritime law perspective. Iran’s assertion of authority to inspect or restrict certain vessels on security grounds maintains a degree of internal legal consistency within its own established position.
Yet the most critical dimension is whether such restrictions can be linked to the right of self-defence. As previously established, if one accepts that Iran has been subjected to armed attacks by the US and Israel, its right to self-defence under Article 51 of the UN Charter is clearly triggered. In this framework, measures taken by Iran to limit not only direct military targets but also the enemy states’ military logistics, supply chains, and strategic mobility can be evaluated within the broader operational scope of self-defence.
From this perspective, the restriction of vessels passing through the Strait of Hormuz that are directly linked to the belligerent states—for instance, those carrying military hardware, serving military purposes, or possessing strategic importance in the context of the conflict—could be argued by Iran as a defensive ‘maritime control’ measure. Such actions bear a certain resemblance to long-accepted instruments in the law of naval warfare, such as blockade, visit, and search.
Nonetheless, the legality of such restrictions is not boundless. Foremost, any measures taken must comply with the principles of necessity and proportionality. Furthermore, general and indiscriminate restrictions on purely civilian vessels with no direct link to the conflict would constitute grave violations of both international maritime law and international humanitarian law. Given that a substantial portion of global energy trade transits through this strait, the risk of wide-scale obstruction creating disproportionate effects on the international community is significant.
In conclusion, while the normative structure suggests that the Strait of Hormuz should remain open under the transit passage regime, this remains legally contested for Iran due to its non-party status to UNCLOS and its position as a persistent objector. This creates a foundation upon which Iran could, under specific circumstances, render its restrictions on certain vessels legally defensible. However, the characterisation of such measures as legitimate self-defence remains strictly contingent upon a rigorous satisfaction of the criteria of necessity, proportionality, and the military nature of the target in every concrete instance. Otherwise, such restrictions will be deemed violations that exceed the limits of self-defence and conflict with the fundamental tenets of international maritime law.
Conclusion
Whilst international law has not succeeded in eradicating war, it has established a normative architecture aimed at limiting the arbitrary use of power by binding it to stringent rules. At the heart of this architecture lie the prohibition on the use of force and its sole exception, the right to self-defence—a pair that maintains a delicate balance between states’ security concerns and the stability of the international order. However, recent developments demonstrate that this equilibrium is being increasingly strained, as interpretations based primarily on ‘perceptions of threat’ strengthen the tendency to stretch legal boundaries.
The intervention by the United States and Israel against Iran serves as a concrete manifestation of the expansion of the concept of self-defence, transforming it almost into a doctrine of preventive war. Conversely, Iran’s response illustrates how a legally recognised right can rapidly evolve into a much broader conflict dynamic. This relationship of reciprocity produces a chain of consequences affecting not only the belligerent parties but also third states, international maritime routes, and global economic stability.
The fundamental issue is not merely whether a specific action is individually lawful, but rather the long-term impact that such interpretations will have on the international legal order. In an environment where the boundaries of the right to self-defence become blurred and subject to subjective security assessments, the normative weight of the prohibition of the use of force will inevitably erode. This carries the risk of regressing the international system into a power-based arena of rivalry.
Consequently, the current crisis should be understood not only as a regional military escalation but also as a critical test of international law’s future. If legal norms continue to be reinterpreted through the progressive expansion of exceptions, the distinction between rule and exception will erode. Ultimately, this situation risks reducing international law to a tool for power politics under the guise of legal legitimacy.
