The move, which could have serious consequences in relations with one of the most powerful nations in the Islamic world, signalled the end of two years of intense diplomacy aimed at persuading Tehran voluntarily to curb its nuclear ambitions.

The endgame will be played out today and tomorrow at a meeting of the 35-nation International Atomic Energy Agency (IAEA) in Vienna, where the states of the European Union look likely to support America’s longstanding demand that Iran be referred to the UN Security Council. Tehran raised the stakes still further yesterday by threatening to resume uranium enrichment if that happened.

Any hope of a compromise was shattered over the weekend when President Ahmadinejad, the newly elected Iranian leader, used his maiden speech before the UN General Assembly to attack the West and declare his intention to build a civilian nuclear industry, which many suspect is a cover for acquiring an atomic bomb.

“If some try to impose their will on the Iranian people through resort to a language of force and threat with Iran, we will reconsider our entire approach to the nuclear issue,” said Mr Ahmadinejad, who accused the West of trying to enforce “nuclear apartheid”.

Jack Straw, the Foreign Secretary, who listened to the speech in New York, described it as disappointing and unhelpful. He was holding discussions with counterparts from other key countries yesterday on what concerted action should now be taken.

“We need to get a feel of whether now is the right time to push for a referral or not,” a British diplomat close to the negotiations said. “We might be able to get a majority at the IAEA. Jack Straw is sounding out his counterparts on where they stand.”

Officials in Vienna believe that 20 members of the IAEA would support action against Iran. Those in favour include the United States, the EU, Japan and Australia, Singapore and Peru.

However, the move would split the organisation in half with opposition from Non-Aligned Movement states including India, Brazil and South Africa. China, which relies heavily on imports of Iranian oil, is also opposed as is Russia, which has the contract to build Iran’s multibillion-pound nuclear reactor at Bushehr.

One possible outcome is that the 14 non-aligned states would abstain in a vote. As of last night, only Russia and Venezuela had decided to vote against.

Mohamed ElBaradei, the head of the IAEA, is still hoping for a deal. He wants Iran to be given one more chance to comply with its commitments to the IAEA.

In return there were reports yesterday that Tehran may allow UN experts to question senior Iranian military officials and visit closed military sites.

At the heart of the dispute is Iran’s insistence on building a nuclear “fuel cycle” to supply civilian nuclear reactors.

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