Research by International Atomic Energy Agency (IAEA) has found Iran’s stockpile of low-enriched uranium has now reached 2.4 tonnes (2,442.9kg). Under the terms of the 2015 Iran Nuclear Deal, Tehran is limited to 202kg. The watchdog also claimed Iran had violated purity levels of enriched uranium with 4.5 percent recorded – above the 3.67 percent limit.
Authorities in Iran have granted IAEA inspectors access into two of its nuclear facilities since August.
The report also found a first cascade of advanced centrifuges have been moved from an above-ground plant to an underground site, in another apparent breach of the accord.
The relocation is understood to have been done after an above-ground facility was destroyed during an attack in the city of Natanz in July.
Iran has defended its nuclear programme and insisted it is there to maintain peace in the region.
The watchdog has since rejected the explanation from Tehran.
The report said: “The agency informed Iran that it continues to consider Iran’s response to be not technically credible.”
It added: “A full and prompt explanation from Iran regarding the presence of uranium particles of anthropogenic origin … at a location in Iran not declared to the Agency, is needed.”
After details of the report emerged, Iran’s ambassador to the IAEA fired back with a stern response.
Gharib Abadi insisted “any hasty comments should be avoided”.
He added: “Interactions are ongoing with a view to finalise the resolution of the matter.”
During a UN General Assembly meeting, Iranian ambassador Majid Takht Ravandchi added Iran and the IAEA “have agreed to work in good faith”.
The Iran Nuclear Deal signed by leading nations including the UK, China and Russia, granted Iran sanction relief in return for curbs on its nuclear weapons programme.
Mr Zarif added: “If we wanted to do that we would have done it with President Trump four years ago.”
Mr Biden has said returning to Iran nuclear deal would be “a starting point for follow-on negotiations”
Writing for CNN in September, he said: “If Iran chooses confrontation, I am prepared to defend our vital interests and our troops.
“But, I am ready to walk the path of diplomacy if Iran takes steps to show it is ready too.”