Iran has stepped up its production of highly enriched uranium in recent months, according to a report by the International Atomic Energy Agency (IAEA) seen by AFP on Saturday.
Tensions between Iran and the UN nuclear watchdog have repeatedly flared since a 2015 deal curbing Tehran's nuclear programme in exchange for sanctions relief fell apart.
The IAEA's latest report comes as Tehran pursues delicate negotiations with the US on its nuclear programme.
It said in its quarterly report that it is of “serious concern” that Iran has an estimated amount of 408.6 kilograms enriched to up to 60 per cent as of May 17, up by 133.8 kilograms since the last report in February.
Uranium enriched to up to 60 per cent fissile purity is close to the roughly 90 per cent level needed for atomic weapons.
According to the IAEA, Iran is the only non-nuclear weapon state to enrich uranium to 60 per cent.
Western governments have for decades suspected Iran of trying to develop a nuclear weapons capability to counter Israel's widely suspected but undeclared arsenal. Iran maintains that its nuclear programme is entirely peaceful and insists it has no intention of developing nuclear weapons.
In a separate in-depth report, the IAEA criticised “less than satisfactory” co-operation from Tehran over its scrutiny of Iran's nuclear programme.
“While Iran continues to co-operate with the agency on matters of routine safeguards implementation, in a number of respects … its co-operation with the agency has been less than satisfactory,” the report said.
It specifically notes Tehran's lack of progress in explaining nuclear material found at undeclared sites.
“In particular, Iran has repeatedly either not answered, or not provided technically credible answers to, the agency's questions and has sanitised locations as listed in this report, which has impeded agency verification activities.”
Iran said the report is “politically motivated and repeats baseless accusations”, state media said.
It said Iran will “implement appropriate measures” in response to any effort to take action against Tehran at a meeting of governors at the IAEA.
Iran's Foreign Minister Abbas Araghchi said earlier on Saturday that his country considers nuclear weapons “unacceptable”, reiterating its long-standing position amid delicate negotiations with the US.
“If the issue is nuclear weapons, yes, we too consider this type of weapon unacceptable,” Mr Araghchi, Iran's lead negotiator in the talks, said in a televised speech. “We agree with them on this issue.”
The US and Iran have held five rounds of talks in Oman and Rome over the past few weeks, aiming to revive or replace the 2015 nuclear deal with world powers, which President Donald Trump withdrew the US from during his first term, in 2018.
These discussions, mediated by Oman, have centred on Iran's uranium enrichment levels, the lifting of US sanctions and the implementation of nuclear inspections.
While both sides have described the talks as constructive, significant disagreements remain, particularly regarding Iran's insistence on its right to enrich uranium and the US demand for a complete halt to this activity.
This week, Mr Trump said his administration was “very close to a solution” on an Iran nuclear agreement. He also said he had warned Israeli Prime Minister Benjamin Netanyahu against a military strike on Iran, which would set back Washington's efforts to broker a deal.
Mr Trump's comment came after Israel dismissed as “fake news” a report by The New York Times, which said Mr Netanyahu had been threatening to sabotage the US-Iran talks by attacking Tehran's nuclear enrichment sites.
“We're very close to a solution now,” Mr Trump added. “Now, that could change at any moment – it could change with a phone call but, right now, I think [Iran] want to make a deal.”
