WHILE THE DUST OF THE IRAN-ISRAEL-US may have temporarily settled under the shadow of a fragile ceasefire, the legal controversies it has stirred will likely reverberate through international legal discourse for years to come. On the night of June 12, 2025, Israel launched airstrikes across Iran targeting its principal nuclear facilities. The United States (U.S.) joined the campaign on June 22 by bombing key Iranian nuclear sites. Israeli Prime Minister Benjamin Netanyahu characterised these operations as acts of legitimate self-defence against an existential threat, while U.S. President Donald Trump justified them as necessary pre-emptive measures to prevent Iran from acquiring nuclear weapons. In sharp contrast, Iran condemned the attacks as flagrant violations of international law. Amid these competing claims, this article seeks to assess whether the Israeli and U.S. attacks on Iran conform to contemporary international law governing the use of force.
The international legal framework governing the use of force
The legal framework regulating the use of force in international relations is rooted primarily in the Charter of the United Nations (‘UN’) and is supplemented by customary international law, much of which has attained the status of jus cogens, as affirmed by the International Court of Justice (‘ICJ’) in Nicaragua v. United States (1986). At the core of this normative framework lies Article 2(4) of the UN Charter, which unequivocally obliges all member states to refrain 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 UN.
There are, nonetheless, two notable exceptions under the UN Charter to this general prohibition on the use of force. First, under Article 42, the Security Council is authorised to undertake collective military action after determining, in accordance with Article 39, that there exists a threat to the peace, a breach of the peace, or an act of aggression, and when other measures (such as those set out in Article 41) are deemed inadequate. Secondly, under Article 51, states possess the inherent right of individual or collective self-defence if an armed attack occurs. However, this right is constrained by the principles of necessity and proportionality, and endures only until the Security Council takes measures to restore international peace and security.
At the heart of the present controversy lies the interpretation of Article 51 of the UN Charter. Both the text of the Charter and the jurisprudence of the ICJ underscore the restrictive nature of this exception. For instance, in Oil Platforms (2003), the ICJ affirmed that the right of self-defence is triggered only by an actual armed attack; mere threats, hostile rhetoric, or uncertain future risks do not qualify. This interpretation reflects the Charter’s intention to narrow the circumstances in which unilateral force may lawfully be employed.
Despite this, some states and legal scholars advocate a broader reading of Article 51. They contend that states should not be required to wait passively until an attack occurs, and that self-defence may be invoked even before an aggressor actually uses force. This broader interpretation has given rise to various concepts—anticipatory, pre-emptive, and preventive self-defence—which differ primarily in their temporal proximity to the perceived threat. Most prominent among the scholars who support a broader understanding of the right of self-defence is Yoram Dinstein, who argues that there is no legal requirement to “wait for the bombs to fall” if it is evident that an armed attack is already underway. Similarly, the United States has long maintained that international law recognises a right to act in self-defence against threats posing an imminent danger, even if an actual attack has not yet materialised.
Nevertheless, this broader interpretation of the right of self-defence—extending to anticipatory, pre-emptive, and preventive self-defence—remains highly contested. The most controversial of these is preventive self-defence: the use of force to eliminate distant or potential threats before they have materialised. The ICJ has never explicitly endorsed such a doctrine, and many states, particularly those from the Global South, reject it as a “relic of the past”, favouring a strict textual reading of Article 51. The UN High-Level Panel on Threats, Challenges and Change, in its 2004 report, also explicitly rejected this broader interpretation. Even where it is cautiously accepted, as in certain legal circles, its scope remains extremely limited. It must conform to the stringent criteria articulated in the Caroline Doctrine (1837), which requires that the necessity of self-defence be “instant, overwhelming, leaving no choice of means, and no moment for deliberation.” Moreover, any use of force must not be “unreasonable or excessive.”
In official statements following the strikes, Israeli Prime Minister Benjamin Netanyahu justified Operation Rising Lion as a necessary act of self-defence aimed at preventing Iran from acquiring nuclear weapons. He described Iran’s nuclear programme as an existential threat to Israel’s survival and stated that the operation was designed to eliminate this threat before it could materialise. To comply with procedural requirements, Israel also submitted a formal letter to the UN Security Council invoking Article 51 of the UN Charter, asserting its right to self-defence against an imminent attack.
Since Israel had not suffered an armed attack prior to its strikes on Iran, it justified its actions by invoking the doctrine of anticipatory self-defence. It contended that the threat posed by Iran's advancing nuclear capabilities was both imminent and existential, maintaining that delaying a response until an actual armed attack occurred would have entailed unacceptable strategic risks. In its official justification, Israel asserted that credible intelligence assessments indicated Iran was on the verge of launching a nuclear-armed strike, and the June 2025 operation constituted the last feasible window to neutralise the threat before it became operationally irreversible. Furthermore, Israel underscored that it had exhausted all diplomatic channels and engaged in prior consultations with key international partners - a deliberate effort to demonstrate that the strikes were neither unilateral nor precipitous, but rather following sustained but unsuccessful efforts to resolve the crisis through non-military means. From Israel’s perspective, the use of force was not only necessary and proportionate but also time-sensitive, a last-resort preventive act to avert catastrophic harm.
At the core of this normative framework lies Article 2(4) of the UN Charter, which unequivocally obliges all member states to refrain 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 UN.
Nonetheless, neither Israel's alarm regarding Iran's nuclear ambitions nor its justifications were novel. For over three decades, Prime Minister Netanyahu has persistently asserted that Iran stands on the verge of developing nuclear weapons, yet the majority of these claims remain unsubstantiated. The International Atomic Energy Agency (IAEA) – the sole international organisation possessing both the mandate and technical expertise to evaluate nuclear programmes – has maintained that Iran discontinued its nuclear weapons programme in 2003. While Iran has enriched uranium beyond the 60% threshold and retains the technical capacity to achieve weapons-grade enrichment levels, the IAEA has never confirmed that Iran has acquired a nuclear weapons capability. Significantly, Israel's current rationale mirrors the justification proffered for its 1981 strike on Iraq's Osirak reactor and its 2007 bombing of Syria's Al Kibar facility, both of which thwere similarly characterised as pre-emptive measures to prevent nuclear weaponisation.
Similarly, President Donald Trump defended the June 22 US precision airstrikes—which reportedly destroyed Iranian nuclear enrichment facilities—as a “limited and necessary use of force to support an ally under threat.” In televised remarks and a formal June 23, letter to the President of the UN Security Council, the US invoked Article 51 of the UN Charter, framing the strikes as collective self-defence against an imminent armed attack on Israel, allegedly enabled by Iran’s nuclear programme. The administration argued that the unique risks of nuclear proliferation justified military action under a broader standard of imminence than would generally apply in conventional warfare scenarios.
The US rationale appears to draw upon the logic underpinning the 2002 U.S. National Security Strategy (commonly referred to as the Bush Doctrine), which endorsed pre-emptive action in response to emerging threats, particularly those involving terrorism and weapons of mass destruction. Although the 2025 strikes were officially described as anticipatory rather than preventive, the legal boundary between these concepts remains inherently ambiguous. U.S. defence officials maintained that Iran’s nuclear facilities were “on the cusp of operationalisation,” asserting that any failure to act would have constituted a dereliction of their responsibility to uphold international peace and security.
This formulation portrays the US strikes as derivative in nature, legally contingent upon the validity of Israel’s invocation of the right of self-defence. In essence, the lawfulness of the U.S. operation presupposes that Israel’s resort to force was itself consistent with international law. However, as affirmed by the ICJ in the Nicaragua v. United States case (1986), the exercise of collective self-defence is justifiable only where the requesting state has been the victim of an actual armed attack. If Israel's operation is found to have lacked this foundational requirement, then the U.S. claim to collective self-defence becomes legally untenable.
As noted earlier, both Israel and the US, along with certain scholars, have sought to justify military strikes against Iran’s nuclear facilities as lawful exercises of self-defence against an “imminent” threat posed by Iran’s nuclear programmes, characterising them as a “measure of last resort.” They further argue that the Caroline standard of imminence must be reinterpreted in the nuclear context, given the potentially catastrophic consequences of inaction. Yet once stripped of rhetorical flourish, these justifications fail to withstand serious legal scrutiny.
In the present case, however, neither the US nor Israel had suffered an armed attack by Iran nor had it issued direct threats to attack them. Thus, the threshold set by Article 51 was not met. Their reasoning hinged instead on a broader view of security, treating even the mere potential of an adversary’s capability as justification for pre-emptive action. This stretches the concept of self-defence beyond the bounds of international law. The strikes thus appear driven more by a speculative future risk than an actual imminent threat, undermining the core legal basis for invoking self-defence.
It must be noted that the legal bar for anticipatory self-defence is high for good reason. The Caroline standard, reaffirmed in the Caroline case and the ICJ’s 1996 Advisory Opinion on Nuclear Weapons, require that force be the only and least harmful means to avert a grave and imminent danger. Although Iran had enriched uranium beyond 60%, yet there was no evidence it had weaponised its nuclear programme, let alone prepared an attack. The IAEA had found no concrete evidence of a nuclear breakout. Israel’s claim of secret intelligence pointing to an imminent attack was neither shared with the Security Council nor corroborated by independent bodies. Worse still, neither Israel nor the US had exhausted diplomatic or peaceful alternatives. No emergency Security Council session was called. No last-ditch negotiations attempted. These omissions cast serious doubt on whether force was truly a last resort.
From Israel’s perspective, the use of force was not only necessary and proportionate but also time-sensitive, a last-resort preventive act to avert catastrophic harm.
What Israel and the US are really instead advocating is preventive self-defence, a doctrine that justifies the use of force to counter a threat that is neither imminent nor certain. Yes some states, such as Germany, France, Japan, and Switzerland, showed limited openness to this doctrine after 2002, but consistently insisted upon the requirement of imminence. None endorse the striking of a country simply because it might one day pose a threat, fearing that it would “unravel the UN Charter.” The notion of preventive self-defence has no place under the UN Charter and prevailing state practice. The overwhelming majority of the international community not only oppose the preventive military action they even regard it a potential act amounting to aggression. Thus, the legality of a preventive strike on Iran cannot be justified on unilateral interpretations of international legal principles by a handful of states.
Given that Iran does not currently possess nuclear weapons, is not immediately capable of producing them, and shows no verified move toward weaponisation, neither Israel nor the US can lawfully justify their strikes under Article 51. Launching attacks on the basis of speculative intelligence and distant threats and in the absence of a clear and imminent armed threat fails to meet the legal threshold for self-defence. Without Security Council authorisation and lacking an actual or imminent armed attack, such use of force violates Article 2(4) of the Charter. The ICJ’s judgments in Nicaragua (1986) and the Oil Platforms case (2003) reinforce that pre-emptive or preventive force not grounded in imminence is unlawful.
The most damning rebuttal to Washington and Tel Aviv’s reasoning comes from their own past statements. When Russia invaded Ukraine in 2022, claiming it was acting in “anticipatory self-defence” against NATO expansion, both the US and Israel rightly dismissed it as legal nonsense, affirming the centrality of imminence. The US State Department even issued a crisp reminder: “Self-defence does not cover speculative threats.”
Yet now, with Iran, the script has flipped. The same governments that condemned Moscow for its “pretextual war” are peddling near-identical arguments. The inconsistency is glaring—and it undermines the credibility of the self-defence regime, opening it to accusations of double standards.
Finally, if the world accepts that states may lawfully bomb each other based solely on another’s capabilities or speculative intentions, rather than concrete acts, it would usher in an era of perpetual conflict. Mere capability does not establish imminence; nor does it provide a lawful basis for defensive war under international law. Instead, such an expansive notion of self-defence would render the UN Charter’s founding purpose — to end the scourge of arbitrary war — effectively meaningless.
Israel’s use of force against Iran, later joined by the US, constitutes a clear breach of international law. While Iran’s nuclear programme raises valid concerns, they do not, by themselves, justify unilateral military action. Without clear Security Council authorisation or evidence of an imminent armed attack, such strikes not only violate international law, they may well constitute acts of aggression under the UN Charter.
Under international law, preventive military action, however strategically justified, is unlawful. Even under the broadest interpretations of the requirement of imminence, the threshold is not met here, as no credible evidence has been presented to show that Iran had weaponised its nuclear programme or intended to deploy such weapons against Israel or the US. The right of self-defence cannot be invoked simply on hostile rhetoric, proxy activities, or speculative fears of a future nuclear breakout.
Given that Iran does not currently possess nuclear weapons, is not immediately capable of producing them, and shows no verified move toward weaponisation, neither Israel nor the US can lawfully justify their strikes under Article 51.
Accepting such reasoning would undermine jus ad bellum, risking its collapse. If force were permitted on the basis of subjective assessments of intent, it would open the floodgates to perpetual conflict, as numerous states possess advanced weapons programmes that rivals might view as a threat. The US-Israel strikes risk setting a wrong precedent that other states might invoke to justify unlawful military actions under the pretext of self-defence, eroding the UN Charter’s foundational principles and global commitments to peace, security, and legal restraint.