Under a 2015 nuclear deal with world powers, Iran was not permitted to enrich uranium above 3.67% purity – the level required for fuel for commercial nuclear power plants – and was not allowed to carry out any enrichment at its Fordo plant for 15 years.
However, Trump abandoned the agreement during his first term in 2018, saying it did too little to stop a pathway to a bomb, and reinstated US sanctions, which crippled the Iranian economy.
Tehran retaliated by increasingly breaching restrictions under the deal, particularly those related to the production of enriched uranium, which is used to make reactor fuel but also nuclear weapons.
US officials, quoted by American media, have said Iran must stop enriching uranium, limit its missile programme and stop supporting proxy groups in the Middle East, as part of a new nuclear deal.
The last time the US took action against Iranian nuclear sites was June last year, when it targeted three uranium enrichment facilities in Iran: Fordo, Natanz and Isfahan.
US officials then said the operation – codenamed “Midnight Hammer” – had significantly set back the prospect of Tehran building a nuclear weapon.
However, Hassan Abedini, the deputy political director of Iran’s state broadcaster, claimed that the country “didn’t suffer a major blow because the materials had already been taken out” of the facilities.
In retaliation, Iran launched missiles on a US military base in Qatar – an attack described by Trump as “very weak” and “expected”.
Additional reporting by Joshua Cheetham, Matt Murphy, Alex Murray, Barbara Metzler and Sofia Ferreira Santos.