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Back to International armed conflict between Iran and the United States

Iran – United States

Reporting period: July 2024 - June 2025

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Conflict Overview

There was a short-lived but intense IAC between Iran and the United States in June 2025. Following attacks by Iran and Israel on each other’s territory in October 2024, tensions surrounding Iran’s nuclear activities erupted once again into an IAC between the two States in June 2025. On 21 June, the United States initiated an overnight bombing campaign on Iranian nuclear facilities. The bombing involved more than 125 US aircraft and 75 precision-guided munitions.1T. Mackintosh and N. Yousif, ‘What we know about US strikes on three Iranian nuclear sites’, BBC, 22 June 2025 (Updated 23 June 2025); ‘History of US-Iran relations: From the 1953 regime change to Trump strikes’, Explainer, Al Jazeera, 23 June 2025. That this amounted to an act of aggression under the rules governing inter-State use of force (jus ad bellum) does not affect the legal analysis under IHL.

Twelve GBU-57 Massive Ordnance Penetrators (MOPs) – known colloquially as ‘bunker-buster bombs’ – were dropped by six B-2 bombers on the Fordo site, a facility buried deep below a mountain. Navy submarines fired thirty cruise missiles against the sites at Natanz and Isfahan while a B-2 bomber dropped two bunker-busting bombs on Natanz.2F. Fassihi, D. E. Sanger and A. Boxerman, ‘What to Know About the U.S. Strike on Iran and the Israel-Iran Cease-Fire’, The New York Times, 12 June 2025 (Updated 24 June 2025). The US attacks during the night of 21 to 22 June 2025, codenamed Operation Midnight Hammer,3D. Vergun, ‘Defense Agency Contributed Toward Operation Midnight Hammer Success’, DOD News, US Department of Defense, 10 July 2025. inflicted significant damage on the facilities at Fordo, Isfahan, and Natanz.4T. Mackintosh and N. Yousif, ‘What we know about US strikes on three Iranian nuclear sites’, BBC, 22 June 2025 (Updated 23 June 2025). They were followed by a riposte by Iran on a US military base in Qatar on 23 June 2025.

In the immediate aftermath of the strikes, a spokesperson for the US Department of Defense claimed that all three sites had sustained ‘extremely severe damage’, although the extent of the damage to Iran’s nuclear programme appeared more limited. The conflict marked the first time that the United States had struck Iranian territory directly, and the first real-world use of the US GBU-57 bombs. These were said to be the only munitions that could reach Iran’s deeply buried nuclear sites.5Council on Foreign Relations, ‘1953–2025 U.S. Relations With Iran’, undated but accessed 21 July 2025. The Iranian Atomic Energy Organization described the bombing of the three nuclear sites as a ‘barbaric violation’ of international law.6T. Mackintosh and N. Yousif, ‘What we know about US strikes on three Iranian nuclear sites’, BBC, 22 June 2025 (Updated 23 June 2025).

The IAC was related to, but was also distinct from, the IAC between Iran and Israel on 13–24 June 2025 discussed above. The conflict between Iran and the United States represents a significant escalation of the long-standing enmity between the two nations that dates back to the 1979 Islamic Revolution in Iran and the so-called ‘Iran hostages crisis’.7‘History of US-Iran relations: From the 1953 regime change to Trump strikes’, Explainer, Al Jazeera, 23 June 2025.

Conflict Classification and Applicable Law

Both Iran and the United States are party to the four Geneva Conventions of 1949, but neither is a State Party to Additional Protocol I of 1977, although Iran has signed it. Customary IHL on the conduct of hostilities applies to the IAC between the two States.

The initiation of Operation Midnight Hammer on 21 June by the United States was the start of the IAC with Iran. Even though it was a short-lived armed conflict, the use of force employed by the United States clearly meets the test set out in the  decision by the Appeals Chamber of the International Criminal Tribunal for the former Yugoslavia (ICTY) in the Tadić  case on the criteria for the existence of an IAC.8ICTY, Prosecutor v Dusko Tadić, Decision on the Defence Motion for Interlocutory Appeal on Jurisdiction, (Appeals Chamber) (Case No IT-94-1-AR72), 2 October 1995, para 70. See also ICRC, ‘How is the term “armed conflict” defined in international humanitarian law?’, Opinion Paper, 2024, pp 9–10.

The IAC in June 2025 was not a continuation of the hostilities between Iran and the United States five years earlier. In 2020, during Donald Trump’s first presidential term, the United States killed General Qassem Soleimani, the head of the elite Quds Force of Iran’s Islamic Revolutionary Guard Corps (IRGC), in a drone strike in Baghdad. In 2019, under US domestic law the US administration had declared the Quds Force to be a foreign terrorist organisation. Iran responded to the assassination of General Soleimani with strikes on US assets in Iraq.9‘Qasem Soleimani: US kills top Iranian general in Baghdad air strike’, BBC, 3 January 2020.

On 23 June 2025, in an apparently managed retaliation for the US strikes on its nuclear facilities,10N. Paton Walsh, ‘A weakened Tehran lashes out performatively against US airbases to save face’, CNN, 23 June 2025. Iran launched missiles against Al Udeid Air Base in Qatar. The attack, codenamed Operation Glad Tidings of Victory (Operation Bashayer Al-Fath in Farsi), did not cause any casualties.11‘Axios: Iran launches six missiles toward US bases in Qatar’, Reuters, 23 June 2025. Iran had reportedly coordinated the attacks on the air base with Qatari officials and gave advance notice that attacks were coming in order to minimize casualties. As The New York Times reported, officials had also said that Iran needed to strike back at the United States for symbolic reasons, but at the same time proceed in a way that allowed all sides an exit ramp. They described it as a similar strategy to that in 2020, when Iran gave Iraq advance warning before firing ballistic missiles at an American base in Iraq after the assassination of General Suleimani.12Fassihi et al, ‘What to Know About the U.S. Strike on Iran and the Israel-Iran Cease-Fire’.

Although there was no formal ceasefire between Iran and the United States, an IAC is deemed to have ended with the general close of military operations. According to the commentary on Common Article 2 of the Geneva Conventions by the International Committee of the Red Cross (ICRC): ‘Even in the absence of active hostilities, such military operations having a continuing nexus with the international armed conflict will justify maintaining the classification of the situation as an international armed conflict.’13ICRC, Commentary on Art 2, Geneva Convention I, 2016, para 279. At the time of writing, however, no further military action had been conducted by either party since 23 June. The IHL in Focus project therefore treats the IAC as having ended.

Neither Iran nor the United States is a State Party to the Rome Statute of the International Criminal Court. Although both have signed the Statute, the United States subsequently notified the depositary (the UN Secretary-General) that it did not intend to ratify it.14Notification of the United States, 6 May 2002.

Compliance with IHL

The United States directed attacks against civilian objects, specifically the three Iranian nuclear research facilities. Each of these attacks constitutes a serious violation of IHL.15ICRC, Customary IHL Rule 7: ‘The Principle of Distinction between Civilian Objects and Military Objectives’; and Rule 156: ‘Definition of War Crimes’. There were no reports of casualties resulting from the US attacks.16‘Iran Reports No Deaths from U.S. Strikes, 430 People Killed Since Israeli Attacks Began’, Iranwire News, 22 June 2025. The Iranian response – the missiles fired at US military base in Qatar – targeted a military objective under IHL. There were no reports of casualties resulting from the Iranian attack.17Fassihi et al, ‘What to Know About the U.S. Strike on Iran and the Israel-Iran Cease-Fire’; Center for Preventive Action, ‘Iran’s Conflict With Israel and the United States’, Council on Foreign Relations, Last updated 10 July 2025.

Civilian Objects under Attack

Attacks against nuclear facilities

Although the United States is not a party to Additional Protocol I, it is a customary rule that: ‘Particular care must be taken if works and installations containing dangerous forces, namely dams, dykes and nuclear electrical generating stations, and other installations located at or in their vicinity are attacked, in order to avoid the release of dangerous forces and consequent severe losses among the civilian population’.18ICRC, Customary IHL Rule 42: ‘Works and Installations Containing Dangerous Forces’. But as discussed above, nuclear facilities other than nuclear power plants fall outside the scope of the rule.19Ibid, citing G. Corn and S. Watts, ‘Protection of Nuclear Facilities in Warfare under International Law’, Joint PIJIP/TLS Research Paper Series, American University Washington College of Law, December 2024.

Under the customary IHL rules of targeting, for Iran’s nuclear facilities to constitute a lawful military objective, it would need to be clear that they were being used to develop weapons – in this case a nuclear explosive device – a factually controversial issue. The US targeting of the three nuclear facilities in Iran apparently caused significant material damage. The underground uranium enrichment section at Natanz, Iran’s main enrichment facility, was impacted, as was the Isfahan facility, but it was claimed that the greatest damage was inflicted on the Fordo underground facility.20S. Sardarizadeh and T. Spencer, ‘Satellite images reveal new signs of damage at Iranian nuclear sites’, BBC Verify, 25 June 2025. Whether or not this is true is uncertain. As noted, the US attack on the facility employed its GBU-57/B munitions, which are designed to attack hardened and deeply buried targets.21Metis, ‘GBU-57/B MOP Series’, Fenix Insight, undated but accessed 18 July 2025. The following day, Israel hit access routes to the facility.22D. Gritten, ‘Israel says it struck Tehran’s Evin prison and Fordo access routes’, BBC, 23 June 2025.

Even if the nuclear facilities targeted by Israel constituted legitimate military objectives, the principle of proportionality would be a significant constraint. As Zwanenburg has argued, the potential for serious civilian harm arising from radiological release must be considered in considering the expected civilian harm in a proportionality assessment. There was no evidence that radiological fallout resulted from the attacks. The IAEA said in a post on social media site X that it had not detected any increase in radiation levels at key nuclear sites in Iran in the aftermath of the US airstrikes: ‘Following attacks on three nuclear sites in Iran … the IAEA can confirm that no increase in off-site radiation levels has been reported as of this time.’23‘US joins Israel in attacking Iran, strikes Fordow, Isfahan, Natanz sites’, Al Jazeera, 22 June 2025.