Iran has told the United Nations nuclear watchdog it plans to enrich uranium to up to 20% purity, a level it achieved before its 2015 accord, at its Fordow site buried inside a mountain, the agency has said. The move is the latest of several recent announcements by Iran to the International Atomic Energy Agency that it plans to further breach the deal, which it started violating in 2019 in retaliation for Washington’s withdrawal from the agreement and the reimposition of US sanctions against Tehran. This step was one of many mentioned in a law passed by Iran‘s parliament last month in response to the killing of the country’s top nuclear scientist, which Tehran has blamed on Israel. Such moves by Iran could complicate efforts by US president-elect Joe Biden to rejoin the deal. “It is an additional blow,” a diplomat based in Vienna told AFP. “Iran has informed the agency that in order to comply with a legal act recently passed by the country’s parliament, the Atomic Energy Organization of Iran intends to produce low-enriched uranium up to 20 percent at the Fordow Fuel Enrichment Plant,” the IAEA said in a statement. An IAEA report to member states earlier on Friday obtained by Reuters used similar wording in describing a letter by Iran to the IAEA dated 31 December. “Iran‘s letter to the agency ... did not say when this enrichment activity would take place,” the IAEA statement said. Fordow was built inside a mountain, apparently to protect it from aerial bombardment, and the 2015 deal does not allow enrichment there. Iran is already enriching at Fordow with first-generation IR-1 centrifuges. Iran has breached the deal’s 3.67% limit on the purity to which it can enrich uranium, but it has only gone up to 4.5% so far, well short of the 20% it achieved before the deal and the 90% that is weapons-grade. The deal’s main aim was to extend the time Iran would need to produce enough fissile material for a nuclear bomb, if it chose to, to at least a year from roughly two to three months. It also lifted international sanctions against Tehran. US intelligence agencies and the IAEA believe Iran had a secret, coordinated nuclear weapons programme that it halted in 2003. Iran denies ever having had one. Biden, who takes office on January 20, has signalled Washington would rejoin the so-called Joint Comprehensive Plan of Action aimed at limiting Iran‘s nuclear programme. The deal has been unravelling ever since president Donald Trump dramatically withdrew from it in May 2018 and imposed crippling economic sanctions on Tehran. Germany’s 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”.