On June 13, Israel launched an unprecedented large-scale attack on Iran’s nuclear facilities. Coupled with subsequent attacks carried out by the United States, these actions represented deeply worrisome developments with serious implications for international law, nuclear safety and security, and regional stability. With a ceasefire now apparently holding, it is time to consider pressing questions about the legality of the attacks.
Israel’s objective was clear: to inflict lasting damage on Iran’s nuclear program and to prevent it from acquiring a nuclear bomb. This assumption is supported by the list of targeted facilities.
Despite the scale of the operations, Iranian authorities reported no rise in off-site radiation levels, a claim echoed by the International Atomic Energy Agency. That said, attacks on nuclear facilities are widely regarded as unacceptable by the international community, as the risk of hostilities triggering the release of dangerous forces remains high in such conflicts.
More importantly, Israel’s and the United States’ attacks on Iranian nuclear sites remain legally dubious. Under the UN Charter, the use of force is permitted only in response to an imminent armed attack or in collective defense of another state facing such an attack. For the United States, justifying the strikes on the grounds of an imminent Iranian threat would therefore be a hard sell. Alternatively, the assault could be framed as an act of collective self-defense in support of Israel. But even that line of argument depends on whether Israel’s initial strikes meet the legal threshold for self-defense under Article 51 of the UN Charter—an assessment that turns on the criteria of necessity and proportionality.
Israel’s use of force appears to be aimed at preempting a future nuclear strike by Iran. Under international law, however, the preventive use of force—based on speculative threats or existential fears—has been widely rejected, most notably in the 2003 US invasion of Iraq and Russia’s attempts to justify its war on Ukraine. Even if one accepts a more permissive position allowing anticipatory self-defense against an imminent threat, Israel would still be required to present clear evidence that (a) Iran indeed has both the intent and the means to carry out nuclear strikes against it and (b) there is no other viable way to prevent such an attack.
While Iran’s nuclear program can hardly be described as peaceful, there is currently no public evidence of its intent to build nuclear weapons and use them against Israel. Even US intelligence agencies continue to assess that Iran remains undecided on building a bomb. Under international law, the mere possibility of a state’s pursuing nuclear weapons does not constitute an imminent armed attack. Moreover, the strikes took place amid ongoing negotiations between the United States and Iran, suggesting that diplomatic avenues to avert the crisis were still available.
Thus, lacking a solid legal basis, both Israel’s and the United States’ actions constitute a violation of Article 2(4) of the UN Charter and should therefore be considered unlawful.
As for the nature of the targets—i.e., nuclear installations—international humanitarian law (IHL) offers only limited treaty protection. Article 56 of Additional Protocol I (AP I) provides that “works or installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, shall not be made the object of attack.” Because of the provision’s narrow scope (for which it has been criticized), nuclear sites that do not generate electrical power fall outside its protection. Additionally, Israel is not a party to AP I, and the United States has signed but not ratified it.
Still, general targeting rules under customary IHL apply, and any attack must yield a clear military advantage while minimizing civilian harm. Under Article 52 of AP I, the targeted sites could potentially qualify as legitimate military targets if they were being used to develop weapons, but this would require compelling evidence. Since Iran maintains that its nuclear program and facilities are for exclusively peaceful purposes, the targeted sites should be considered illegitimate military objectives in the absence of proof to the contrary.
While Trump’s decision to bomb Iran’s nuclear sites may lack legal justification, it can be interpreted as a strategic move to decisively eliminate a long-suspected weapons program and prevent Iran from accelerating its nuclear ambitions in response to Israel’s earlier strikes. Whether this strategy succeeds, however, will depend on the outcome of the strikes, particularly on key sites such as Fordow, Esfahan, and Natanz—details that remain unclear.
Dr Maria Kurando is a Visiting Research Fellow working in the Arms Control and Emerging Technologies research area.