Iran said Tuesday it had begun producing uranium enriched to 60 percent at its Fordo plant, an underground facility that reopened three years ago amid the breakdown of its nuclear deal with major powers.
The International Atomic Energy Agency confirmed the move, which Iran said was part of its response to the UN nuclear watchdog's adoption last week of a censure motion drafted by Western governments accusing it of non-cooperation.
"We warned that political pressure and resolutions wouldn't change anything and that the adoption of a resolution would draw a serious response," Atomic Energy Organisation of Iran chief Mohammad Eslami said.
"That's why the production of uranium enriched to 60 percent began at Fordo from Monday."
An atomic bomb requires uranium enriched to 90 percent.
Iran, which had already been enriching uranium to 60 percent at one facility before starting at Fordo, has always denied any ambition to develop an atomic bomb, and insists its nuclear activities are for civilian purposes only.
Under a landmark deal struck in 2015, Iran agreed to mothball the Fordo plant and limit its enrichment of uranium to 3.67 percent, sufficient for most civilian uses, as part of a package of restrictions on its nuclear activities aimed at preventing it covertly developing a nuclear weapon.
In return, major powers agreed to relax sanctions they had imposed over Iran's nuclear programme.
But the deal began falling apart in 2018 when then US president Donald Trump pulled Washington out of the agreement and reimposed crippling economic sanctions.
- 'Deep concern' -
The following year, Iran began stepping away from its commitments under the deal. It reopened the Fordo plant and started enriching uranium to higher levels.
In January 2021, Iran said it was working to enrich uranium to 20 percent at Fordo. Several months later another Iranian enrichment plant reached 60 percent.
The IAEA said in a statement sent to AFP Tuesday that its chief Rafael Grossi "in his latest report to member states... today said Iran had started producing high enriched uranium" at Fordo.
The US expressed "deep concern" over progress Iran is making on its nuclear program and ballistic missile capability.
"We're going to make sure we have all options available to the president," said White House national security spokesman John Kirby.
President Joe Biden has expressed a desire for Washington to return to a revived deal, and on-off talks have been underway since April last year.
Britain, France and Germany -- the European parties to the nuclear deal -- also condemned Iran's expansion of its nuclear programme, saying it had "no credible civilian justification".
Iran has now "taken further significant steps in hollowing out the JCPOA", they said, using an acronym for the accord.
- Response to IAEA censure -
The implementation of the 2015 deal was overseen by the IAEA but the UN watchdog's relations with Iran have declined sharply in recent months.
The IAEA board of governors passed a resolution on Thursday criticising Iran for its lack of cooperation.
The ISNA news agency said that the step at Fordo was one part of Iran's response.
"As well, in a second action in response to the resolution, Iran injected (uranium hexafluoride) gas into two IR-2m and IR-4 cascades at the Natanz plant," it said, referring to an older enrichment facility.
The UN watchdog has been pressing Iran to explain the discovery of traces of nuclear material at three sites it had not declared, a key sticking point that led to the adoption of an earlier censure motion by the IAEA in June.
In a report seen by AFP earlier this month, the IAEA said Iran's stockpile of enriched uranium stood at 3,673.7 kilogrammes as of October 22, a decrease of 267.2 kilogrammes from the last quarterly report.
This included significant stockpiles of uranium enriched to higher levels -- 386.4 kilogrammes to 20 percent and 62.3 kilogrammes to 60 percent.
The heavily protected Fordo plant around 180 kilometres (110 miles) south of Tehran was built deep underground in a bid to shield it from air or missile strikes by Iran's enemies.
The IAEA complains that the ability of its inspectors to monitor Iran's stepped up nuclear activities has been hampered by restrictions imposed by Iran.
Arch foe Israel has never ruled out military action if it deems it necessary to prevent Iran developing a nuclear weapons capability.
Israel is widely suspected to hold the region's sole if undeclared nuclear arsenal, although it has consistently refused to confirm or deny that it is nuclear-armed.
