The statement by the nuclear watchdog, based on a UN document seen by the Associated Press, follows a sharp deterioration in relations between the body and Tehran.
It also comes after a meeting between US President Joe Biden and China’s President Xi Jinping, at the Asia-Pacific Economic Co-operation summit near San Francisco.
At the meeting, Mr Biden said he asked Mr Xi to use his influence with Iran to urge Tehran not to launch proxy attacks on US targets in the Middle East amid the Israel-Gaza war.
It also comes as efforts to return to a 2015 nuclear deal between Western powers and Iran, which allowed an easing of trade sanctions in exchange for UN inspections of nuclear sites and a curbing of uranium enrichment, reached a dead end.
Talks have derailed despite a US deal with Iran to unfreeze $6 billion of frozen funds in exchange for the release of six dual-national American citizens held by Tehran.
Tensions have mounted over Iran supplying thousands of drones and artillery shells to Russia for its war with Ukraine and its continuing support for Hamas following the October 7 attack in southern Israel that killed about 1,200 people.
Iran has also “de-designated” several of the UN nuclear inspectors, said to be experienced in nuclear research, and failed to reinstall cameras put in place by the UN at nuclear compounds for monitoring.
Iran has an estimated 128.3kg of uranium enriched up to 60 per cent purity, increasing by 6.7kg since a September report by the IAEA.
Iran’s overall stockpile of enriched uranium is said to have increased by 691kg, from 3,795.5kg to 4,486.8kg.
The former level would be enough to make several nuclear bombs, IAEA chief Rafael Grossi warned.
Iran is said to be reaching a “breakout” threshold where the technical capacity is in place to create “weapons-grade” uranium enriched to 90 per cent.
A series of technical steps would then be required to create a warhead small enough to be placed on a long-range ballistic missile, a process known as miniaturisation. Iran is said to have been researching this process since the early 2000s. However, one of their leading researchers on the project, Mohsen Fakhrizadeh, was assassinated in 2020, allegedly by Israel.
Mr Biden has said he'd be willing to re-enter a nuclear deal with Iran, but formal talks to try to restart the deal collapsed in August 2022. Former president Donald Trump pulled out of a deal in 2018, saying it did not do enough to curb Iran’s nuclear ambitions.
According to the latest report, Mohammad Eslami, the head of Iran's civilian nuclear programme, reasserted that it was “within its rights to de-designate the Agency inspectors” and stated that the nuclear watchdog's “assertion” of the potential risks of impeding the conduct of inspections ‘is not compelling and lacks any legal basis”.
Mr Eslami added, however, that he was “exploring possibilities to address the request” to reconsider the ban on the inspectors.
The IAEA has said it views as “extreme and unjustified” Iran's decision to withdraw inspectors who come from three European countries that Mr Eslami has reportedly said “regularly demonstrated harsh political behaviours”.