Iran said nuclear diplomacy could crumble if France, Germany and the UK went ahead with a resolution to condemn Tehran’s partial suspension of inspections by the UN’s atomic watchdog.
Censure led by the three European powers would be an expression of "serious concern" at Tehran's refusal to co-operate with International Atomic Energy Agency site inspections from February 23.
It would put a three-month agreement for the IAEA to be allowed some access to Iran's nuclear sites at risk.
It could also damage efforts to persuade Iran to return to the 2015 nuclear deal it agreed with six world powers, known as the Joint Comprehensive Plan of Action, or JCPoA.
"I have to give this warning, that actions against our expectations will have adverse effects on diplomatic processes, and can quickly close the windows of opportunity," Iran's government spokesman Ali Rabiei said.
Iran expected "all parties to act rationally and prudently, and to know the value of fleeting moments," he said. "We are still committed to diplomacy.”
The proposed resolution by the three European powers – known as the E3 - will be put forward during a meeting of the IAEA’s board of governors on Friday and the move is supported by the US, AFP reported.
Separately, the UK government said: “We urge Iran to stop and reverse all measures that reduce transparency and to ensure full and timely co-operation with the International Atomic Energy Agency.”
Iran imposed restrictions on IAEA inspectors after the US refused to lift sanctions imposed by former president Donald Trump.
Tehran agreed a last-minute deal with the IAEA last month to mitigate the loss of some inspections, but it still meant footage from cameras on Iran's nuclear programme will be stored and not given to the agency for up to three months. If sanctions are not lifted by then, the data will be destroyed.
Iran has recently repeatedly breached the JCPoA after Mr Trump withdrew the US from it and reimposed sanctions in 2018.
The administration of US President Joe Biden has strongly suggested a desire to return to the deal, but it has urged Iran to return to its nuclear commitments first.
Iran said it will only do so once the sanctions are lifted.
Europe's three signatories to the JCPoA have urged Iran to return to the accord while condemning its violations of it.
After Tehran rejected the opportunity of an informal meeting with the E3, EU and the US. France said the decision came "at a time when Iran is accumulating JCPoA violations, among other things limiting the IAEA's verification capabilities".
Germany said it was in discussion with France and the UK to ensure constructive talks between the JCPoA’s participants could come about.
In response to Iran’s rejection of the EU’s invitation to talks, the US said it remained ready to engage in “meaningful diplomacy”.
"As we have made clear, the United States is prepared to meet Iran to address the way forward on a mutual return to compliance," State Department spokesman Ned Price said.
"We're not dogmatic about what form that takes. What we are dogmatic about is the underlying commitment that this administration broadly has: that Iran cannot be allowed to acquire a nuclear weapon."
