Relations between Iran and the United States have been characterized by enduring tensions since the 1979 Islamic Revolution and the hostage crisis. More recent frictions centred on Iran’s nuclear programme and closely intertwined with the parallel Iran-Israel armed conflict. In June 2025, following reciprocal Iran-Israel strikes and renewed concerns about Iran’s nuclear activities, the United States launched Operation Midnight Hammer against Iran’s main uranium enrichment facilities at Fordo, Isfahan and Natanz, using ‘bunker-buster’ bombs and cruise missiles. Washington presented the damage as extremely severe, while Iran denounced the operation as a grave violation of international law and responded with missile strikes on the US Al Udeid Air Base in Qatar.
Classifications and Parties to the Conflicts
- International armed conflict between Iran and the United States (late June 2025)
United States (US) strikes hit three Iranian nuclear research facilities, causing significant damage at Natanz and Isfahan and possibly at Fordo. As the alleged military use of these sites to develop a nuclear explosive device remained factually contested, the facilities did not clearly qualify as military objectives and have to be considered civilian objects protected against attack. Accordingly, the strikes were assessed as serious violations of IHL, despite the absence of reported casualties or radiological fallout. Iran’s response, consisting of missile attacks on a US military base in Qatar, was directed at a lawful military objective and caused no reported casualties.
Historical Background
Origins
Relations between Iran and the United States have been marked by enduring tensions since the 1979 Islamic Revolution and the Iran hostage crisis.
Nuclear programme dispute and link to Iran-Israel armed conflict
After reciprocal Iran-Israel strikes in October 2024, tensions over Iran’s nuclear activities rose again in June 2025. The United States (US) overnight bombing campaign occurred in a context closely connected to the simultaneous Iran-Israel hostilities. On 23 June 2025, Iran fired missiles at the United States’ Al Udeid Air Base in Qatar.
Key Developments (2023–2025)
Since October 2024, the situation saw several major developments:
- International Atomic Energy Agency (IAEA) resolution on safeguards obligations: On 12 June 2025, the IAEA Board of Governors adopted a resolution on Iran’s safeguards obligations. It marked the first formal declaration in two decades that Iran was in breach of its nuclear nonproliferation obligations.
- Israel–Iran strikes in June 2025: On 13 June 2025, Iranian state television reported an initial volley of Israeli strikes, with residential areas in Tehran reportedly hit. This initiated a 12-day period of hostilities between Iran and Israel.
- Operation Midnight Hammer: Eight days after the outbreak of the Iran-Israel hostilities, the United States conducted Operation Midnight Hammer against Iran’s principal uranium enrichment facilities. The strikes, lasting a short period, caused significant damage at Fordo, Isfahan, and Natanz and involved bunker buster munitions delivered by B 2 bombers, as well as submarine launched cruise missiles. In the immediate aftermath, U.S. officials asserted extremely severe damage, while Iranian authorities denounced the strikes as a barbaric violation of international law.
International Armed Conflict
Iran vs the US
Both Iran and the United States are parties to the four Geneva Conventions of 1949, but neither is a State Party to Additional Protocol I, although Iran has signed it. An international armed conflict (IAC) arises whenever one or more States resort to armed force against another State. On the night of 21 to 22 June 2025, the United States launched Operation Midnight Hammer, using B2 stealth bombers and submarines to strike Iranian nuclear installations at Esfahan, Fordo and Natanz, thereby triggering an IAC. This IAC cannot be considered as a continuation of the 2019-2020 hostilities linked to the US killing of General Qassem Soleimani (commander of elite Quds Force of Iran’s Islamic Revolutionary Guard Corps (IRGC)) and Iran’s retaliatory strikes on US assets in Iraq. On 23 June 2025, Iran fired missiles at the US Al Udeid Air Base in Qatar without casualties, reportedly with prior notice and coordination with Qatar to minimize harm. Although no formal ceasefire followed between Iran and the United States, the absence of further military operations after 23 June warrants to consider that the IAC between Iran and the United States has come to an end.
Key Parties to the Conflict
State Parties
- Iran
- The United States
ATTACKS ON CIVILIAN INFRASTRUCTURE
The United States struck three Iranian nuclear research facilities, identified as civilian objects, and each attack constitutes a serious violation of IHL. No casualties were reported from these strikes. Iran’s response consisted of missile attacks on a United States (US) military base in Qatar, which targeted a lawful military objective under IHL. No casualties were reported from the Iranian attack.
Attack on Nuclear Facilities
Although the United States is not party to Additional Protocol I, customary IHL requires particular care when attacking works containing dangerous forces such as dams, dykes and nuclear power plants (and other installations located at or in their vicinity), while other nuclear facilities fall outside that specific rule. US strikes on three nuclear facilities reportedly caused significant material damage to Natanz and Isfahan and possibly to Fordo sites, using GBU 57/B munitions, which are designed to attack hardened and deeply buried targets. Under general targeting rules, Iran’s nuclear sites would be military objectives only if they were being used to develop weapons – here a nuclear explosive device – which remained factually contested. Proportionality considerations included the risk of radiological release, yet no fallout was evidenced and radiation monitoring reported no off-site increase.