On June 27, 2025, the United States submitted a letter to the UN Security Council outlining its legal rationale for military strikes conducted on June 22 against Iranian nuclear facilities located at Fordow, Natanz, and Isfahan. This marked the first military engagement by the U.S. on Iranian territory, prompting significant scrutiny of the legal justification provided.
Having assisted in drafting such letters regarding the use of military force, many observers find the explanation presented by the U.S. government to be lacking in substantive international legal foundation.
The central argument presented in the U.S. letter hinges on a claim of acting in collective self-defense, relying primarily on Article 51 of the UN Charter, which encompasses the right to self-defense in response to an armed attack against a Member State. However, concerns exist regarding the adequacy of this legal rationale and whether it truly aligns with established norms in international law.
International law, particularly Article 2(4) of the UN Charter, explicitly prohibits the use of force against the territorial integrity or political independence of any state. Article 51, conversely, allows for self-defense, but only in response to an actual armed attack. The U.S. has historically maintained that anticipatory self-defense can be invoked in situations where a viable threat is imminent, though this stance has been met with considerable debate and interpretation over the years.
The legal framework becomes murky when examining the U.S.’s assertion surrounding its right to collective self-defense on behalf of Israel. In its letter, the U.S. articulated that its actions were necessary to protect Israel from what it described as an ongoing and intensified campaign by Iran over several decades. However, critics argue that the justification presented is insufficiently specific and does not meet the criteria established under international law, particularly in demonstrating an immediate necessity for the use of force.
The report issued by the U.S. government failed to adequately establish that peaceful alternatives had been fully explored and exhausted before resorting to military action. The letter suggests that previous diplomatic efforts had been made to address concerns regarding Iran’s nuclear ambitions, but the historical context tells a more nuanced story.
Notably, the unilateral withdrawal of the U.S. from the Joint Comprehensive Plan of Action (JCPOA) in 2018 during President Donald Trump’s administration severely undermined earlier diplomatic frameworks aimed at curtailing Iran’s nuclear capabilities.
Despite the apparent lack of a clear and direct armed attack justifying the military strikes, the U.S. letter also claimed that Iran’s nuclear program posed an imminent threat to both its security and to that of Israel. However, a lack of clarity surrounds what constituted this alleged imminent threat, raising further doubts about the legality of the actions taken.
Additionally, the U.S. letter expressed a concern regarding Iranian-supported proxies attacking Israel, yet failed to provide sufficient attribution of responsibility to Iran regarding these actions. The principles of state responsibility are fundamental in assessing claims of collective self-defense, overshadowing the U.S.’s justification and casting doubts on the legal arguments presented.
Throughout its letter, the U.S. made references to a range of situations within the context of an “international armed conflict,” however, it is important to distinguish between the legality of resorting to force (jus ad bellum) and the conduct of hostilities (jus in bello). The existence of armed conflict does not inherently validate the legality of military action in the absence of a lawful basis for that force.
Critically, numerous legal scholars and practitioners argue that U.S. legal justifications appear to be an attempt at post hoc reasoning intended to rationalize a decision that may have been politically motivated over legally mandated.
The necessity for proactive legal guidance and support from executive branch lawyers is imperative in ensuring compliance with both domestic and international law in matters regarding the use of force. There is an urgent need for legal advisors within the U.S. administration to engage actively in shaping the legal contours of decision-making processes related to military interventions, rather than merely attempting to provide justifications after actions have already been taken.
In conclusion, while the U.S. government sought to frame its military strikes within the bounds of international law, the prevailing legal arguments presented in the Article 51 communication fall short of satisfactory legal standards. As the debate around the legality of the strikes continues to unfold, it highlights the broader implications of using military force in international relations and the resulting responsibilities that come with it.
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