Iran has announced plans to enrich uranium up to 20% purity, just a step away from weapons-grade levels, as tensions with the US ratchet up during the final days of Donald Trump’s presidency. The International Atomic Energy Agency (IAEA) confirmed it had been notified of Iran’s decision to increase enrichment at the Fordow facility, buried in a mountainside to protect it from military strikes, although Tehran did not say when the process would begin. The weekend also marks the first anniversary of a US drone strike that killed top general Qassem Suleimani, with Washington apparently bracing for possible retaliation. After the US stepped up military deployments and threatening language, Iran’s foreign minister, Javad Zarif, accused it on New Year’s Eve of trying to set up a “pretext for war”. In an apparent attempt at de-escalation the Pentagon has abruptly withdrawn the aircraft carrier Nimitz from the region, the New York Times reported. The US president-elect, Joe Biden, has made clear that he hopes to revive the 2015 Iran nuclear deal, known as the Joint Comprehensive Plan of Action, which was abandoned by Trump in 2018. The deal limited Iran to enriching uranium to 3.67%. It also called for Fordow to be turned into a research and development facility. Iran began violating the deal in 2019, in response to America’s withdrawal and imposition of sanctions. But it has also signalled a desire to rejoin the deal, in return for sanctions relief. November’s IAEA report, the latest available, said that Tehran was still allowing inspections, and although it was enriching uranium beyond 3.67%, it was not exceeding a 4.5% threshold. Other signatories of the deal, including the EU, France, Germany, UK, China and Russia, have been playing for time, hoping the agreement could be restored under Biden. The German foreign minister, Heiko Maas, has said the change of administration in the US means that there is “a last window” for progress that “shouldn’t be wasted”. But Biden will be managing a very high-stakes relationship – and attempting to rekindle an always-controversial deal in the face of significant opposition inside both countries – at a time when the domestic fight against Covid is sucking up huge amounts of government time and energy. Iran originally began 20% enrichment under former hardline president Mahmoud Ahmadinejad, heightening concerns that it was pursuing a nuclear weapons programme, although Tehran has always insisted it has only peaceful aims. The 2015 deal aimed to extend the country’s breakout time for creating a nuclear weapon from a few months to at least a year. If Iran resumes the higher level of enrichment, the international tensions that preceded the agreement could return. The latest move came after Iran’s parliament passed legislation following the November assassination of a top nuclear scientist, in an attack blamed on Israel. The new law calls for the country to produce at least 120kg of 20% enriched uranium a year – a key step towards weapons-grade, which is 90% enriched – and put an end to IAEA inspections designed to check its programme is only for peaceful use. Ali Akbar Salehi, the US-educated head of the civilian Atomic Energy Organization of Iran, offered a military analogy to describe his agency’s readiness to take the next step in uranium enrichment. “We are like soldiers and our fingers are on the triggers,” Salehi told Iranian state television. “The commander should command and we shoot. We are ready for this and will produce [20% enriched uranium] as soon as possible.” He said natural uranium in centrifuges at Fordow would need to be switched out for material enriched to 4% if the further enrichment was to proceed. “It should be done under IAEA supervision,” Salehi added. Fordow is nestled in mountains near the holy city of Qom, about 90km south-west of Tehran.