"The production of uranium metal has potentially grave military implications," said the foreign ministers of Britain, France and Germany in a joint statement.

Iran had signed up to a 15-year ban on "producing or acquiring plutonium or uranium metals or their alloys" under the so-called Joint Comprehensive Plan of Action (JCPoA) signed in 2015 with world powers.

"We strongly urge Iran to halt this activity, and return to compliance with its JCPoA commitments without further delay if it is serious about preserving the deal," said the ministers.

Their call came after Iran told the UN nuclear watchdog on Wednesday that it was advancing research on uranium metal production, saying it is aimed at providing advanced fuel for a research reactor in Tehran.

The landmark 2015 deal agreed between Iran and the United States, China, Russia, Britain, France and Germany to curb Tehran's nuclear ambitions has been largely in tatters since President Donald Trump withdrew from it in 2018 and reimposed harsh sanctions.

The Iranian government has signalled a readiness to engage with US President-elect Joe Biden, who takes office on January 20 and who has expressed willingness to return to diplomacy with Tehran.