Iran on Monday denied reports that it has enriched uranium up to 84 per cent, just below the 90 per cent needed to produce an atomic bomb.
The Vienna-based International Atomic Energy Agency (IAEA) said on Sunday evening that it was in discussions with Tehran after Bloomberg News reported that the watchdog's inspectors in Iran last week found uranium enriched to 84 per cent purity.
The report comes with negotiations stalled to revive a landmark deal over Iran's nuclear programme.
Iran was last known to have enriched uranium to up to 60 per cent. Uranium enriched to around 90 per cent purity is considered nuclear weapons-grade.
The spokesman for the Atomic Energy Organisation of Iran, Behruz Kamalvandi, on Monday described the report as "slander" and a "distortion of the facts", according to state news agency IRNA.
"The presence of a particle or particles of uranium above 60 per cent in the enrichment process does not mean enrichment above 60 per cent," he added.
A diplomat confirmed to AFP the 84 per cent reported by Bloomberg, saying "the percentage is correct".
The IAEA is "giving Iran the opportunity to explain because it's apparently possible that there can be so-called 'spikes' of higher levels of enrichment," the diplomat added.
French Foreign Minister Catherine Colonna said her country was in touch with the IAEA to "have more precise information".
France is part of the Iran 2015 nuclear deal together with China, Germany, Russia and the UK.
"It goes without saying that if this press information were confirmed, proven, this would constitute a new and extremely worrying element," she told reporters in Brussels.
Iran's foreign ministry spokesperson Nasser Kanani said on Monday that his country is "committed" to the nuclear non-proliferation treaty and its safeguards agreement with the IAEA.
He warned against the politicisation of the role of the UN nuclear watchdog, saying it "distorts its position".
"The agency should act within the framework of specialised tasks," he added.
The 2015 accord promised Iran sanctions relief in exchange for curbs on its nuclear programme to prevent it from developing a nuclear weapon -- something Tehran has always denied seeking.
But the US unilaterally withdrew from the deal in 2018 and reimposed sanctions on Iran, prompting it to begin walking back on its commitments under the accord.
Negotiations between world powers to return to the deal started in 2021 but have been in deep freeze since last year.
During a telephone call Sunday evening with European foreign policy chief Josep Borrell, Iran's top diplomat Hossein Amir-Abdollahian indicated that a visit by IAEA chief Rafael Grossi to Tehran was still planned.
"If the agency acts with a technical objective and not a political one, it will be possible to agree on a framework to resolve" the nuclear dispute, Amir-Abdollahian said.
Borrell said he asked Amir-Abdollahian during the call to "fulfil their obligation" with respect to the IAEA "because there are some worrying news on the enrichment of uranium".