Donald Trump, president of the United States, announced on his social media that America “completed a very successful attack on the three nuclear sites in Iran, including Fordow, Natanz, and Esfahan.” He further said that “a full payload of BOMBS was dropped on the primary site, Fordow.” After the announcement, Trump addressed it from his Oval Office. He did not provide any explicit legal justification for their action in his social media announcement or his Oval Office address. Iran condemned the US attack as a breach of international law. It said that it would reserve all options to defend its sovereignty, interest and people in accordance with the right of self-defence under the United Nations Charter. Without a clear legal justification from the US, a plausible legal evaluation may be formulated from the US President’s statements. Before these US military strikes, Israel attacked Iran on 13 June 2025, and since then, both countries have been militarily targeting each other. The legal evaluation of US strikes on Iran needs to take into consideration this existing conflict between Israel and Iran, as President Trump said that they worked with Israel as a team during the US attacks on Iran. While it is perturbing to see that the US, a permanent member of the UN Security Council, fails to give legal justification for its military strikes, it is argued here that the US military strikes, along with Israeli attacks, on Iran are contrary to international law.
Use of Force and the UN Charter
The use of force between states is governed by the UN Charter. Article 2(4) of the Charter prohibits the threat or use of force against any state. There are only two exceptions to this prohibition: individual or collective self-defence under Article 51 and the collective security measures authorised by the UN Security Council under Chapter VII of the UN Charter. Article 51 provides that members of the UN have an inherent right of individual or collective self-defence if an armed attack occurs against them. Customary international law further seeks that this right also meets the requirements of necessity and proportionality. Article 51 explicitly says that states have the right of self-defence when an armed attack actually takes place against them.
The recent US attack on Iran’s nuclear sites begs the question: Does it fall under the scope of a state’s right of self-defence, whether anticipatory, preventive or pre-emptive?
However, there have been varied interpretations of the scope of the right of self-defence in the form of anticipatory, preventive or pre-emptive self-defence. While there is no consistency in the use of these terms—anticipatory, preventive or pre-emptive self-defence—in state practice and international law scholarship, the essence of these arguments is that the right of self-defence can be invoked by a state even if the attack has not taken place on it. What is required is to see the possibility of an attack. There is further controversy about when that possibility will become real. An expansive view of this possibility does not focus on the certainty of attack. In other words, this possibility can be boundless in terms of temporality. This expansive view of anticipatory self-defence does not have much support in international law scholarship and state practice. However, a restricted view of this possibility links it to imminence. Arguably, the imminence of an attack is what makes the right of anticipatory self-defence possible. Debates on anticipatory self-defence and the nature and scope of imminence continue in international law scholarship and state practice without any finality. However, what needs to be underlined is that the arguments of anticipatory self-defence, whether expansive or restrictive in terms of temporality and imminence, deviate from the requirements of armed attack under Article 51 of the UN Charter. The danger this deviation poses is that it defeats the purpose of the UN Charter prohibition on the use of force and its collective security system. The purpose of the UN Charter framework on the use of force is to prevent the unilateral use of force in international relations. The right of self-defence is essentially a unilateral measure. Thus, the requirement of an armed attack prior to responding based on the right of self-defence, immediate reporting of the action taken in the exercise of the right of self-defence to the UN Security Council, and customary international law requirements of necessity and proportionality are all the measures intended to restrict the scope of the unilateral use of force. Any form of anticipatory self-defence invariably leaves it to the unilateral decision of a state on the future possibility of an attack on it.
