The UN nuclear watchdog’s board has called on Iran to stop denying inspectors access to two sites in the first censure of its kind for eight years.
The ruling by the International Atomic Energy Agency’s 35-nation board of governors raises pressure on Iran to co-operate but will anger China, which warned even a mild rebuke could unravel global efforts to contain the spread of nuclear weapons.
Iran called the resolution "unconstructive and disappointing", claiming in a foreign ministry statement that it had "the highest level of co-operation with the IAEA".
The ruling came as the foreign ministers of Britain, France and Germany met and repeated their opposition to US tactics.
The Europeans continue to believe the American strategy of putting maximum pressure on Iran will not resolve the differences.
"We have stated unequivocally our regret and concern at the decision by the United States to withdraw... and to re-impose sanctions on Iran," a statement issued via the UK Foreign Office said.
It added: "We firmly believe that any unilateral attempt to trigger UN sanctions snapback would have serious adverse consequences...
“We are convinced that we must address shared concerns about Iran’s nuclear program, its ballistic missile program and its destabilising regional activities in the long term.”
They remain signed up to the 2015 nuclear deal along with China. President Donald Trump pulled the United States out of the Joint Comprehensive Plan of Action in 2018.
Gemany, France and Britain triggered a dispute mechanism in January because of continued Iranian violations of the agreement designed to prevent Tehran from securing nuclear weapons.
The resolution by the board of the nuclear agency tells Iran to let inspectors into the sites mentioned in two reports because they could still host undeclared nuclear material or traces of it.
The text “calls on Iran to fully co-operate with the agency and satisfy the agency's requests without any further delay, including by providing prompt access to the locations specified by the agency”, according to Reuters.
Saudi Arabia welcomed the IAEA board's resolution in a statement issued by the kingdom’s ambassador to Austria, the Wam news agency reported.
Iran has been blocking access to the site for months. Even though the sites in question are not thought to be directly relevant to Iran's current nuclear programme, the agency says it needs to know if activities going back almost two decades have been properly declared and all materials accounted for.
The rebuke was the first of its kind since 2012 but was opposed by China and Russia, another signatory to the deal in a sign of further unravelling of the troubled agreement.
China submitted a five-page statement to the IAEA in Vienna on Thursday, saying the reprimand could demolish “the entire global non-proliferation regime”.
“The root causes of this situation lie in the unilateral and bullying practices of the US,” Beijing envoy Wang Qun said.
Mr Wang said that if the resolution were to pass, it could also mean the end of the 2015 nuclear agreement between Iran and world powers.
France, Britain and Germany are opposed to isolating Iran and believe that the country is likely to return to the negotiating table only when it sees immediate and tangible benefits.
The three countries triggered the deal’s dispute mechanism to try to bring Iran back into compliance after its regular flouting of limits imposed in the agreement.
Tehran had suspended all limits on production of enriched uranium that can be used to make not reactor fuel, but also nuclear weapons.
The UK’s Dominic Raab and his German and French counterparts, Heiko Maas Jean-Yves Le Drian, also discussed China’s proposed new security law in Hong Kong.