They expressed astonishment that widely differing policies — ranging from military action to diplomatic soft-pedalling — were still being debated even as the International Atomic Energy Agency board prepared for its vital meeting in Vienna today.

Iran yesterday raised the stakes by vowing that it would resume large-scale uranium enrichment if the meeting referred the Islamic republic to the UN Security Council.

Condoleezza Rice, the US Secretary of State, who will today hold talks in Washington with Sergei Lavrov, the Russian Foreign Minister, is advocating a cautious approach.

“Nobody has said that we have to rush immediately to sanctions of some kind,” she said at the weekend.

“I think the Security Council will have to have a serious discussion about what the next steps will be.”

Members of the Commons Foreign Affairs Select Committee returning from Washington were, however, confused and disorientated about the direction of US policy towards Iran. They had held talks with John Bolton, the US Ambassador to the UN, who is a hawk on the issue. He told the MPs that he wanted a “Chapter 7 resolution” under which the UN would authorise military action, such as air strikes, against Iran.

Mr Bolton was quoted as saying: “They must know everything is on the table and they must understand what that means. We can hit different points along the line. You only have to take out one part of their nuclear operation to take the whole thing down.”

Mike Gapes, the committee chairman, said that this was one of “at least three views” they had heard on Iran from within the Administration.

Another option, which he ascribed to the Pentagon, where they had talks with Peter Rodman, the Assistant Defence Secretary, and Brigadier-General Carter Hamm, formerly the US commander in northern Iraq, was to throw the issue “into the Security Council like a hand grenade and see what happens”.

However, Mr Gapes said that both the CIA and Richard Lugar, the Republican chairman of the Senate Committee on Foreign Relations, believed that the US should “ride it out” rather than engage in “posturing”, because of a lack of clarity as to what the Security Council would agree. Going to the UN could lead to a rerun of the attempts to get agreement on Iraq before the war.

Ali Larijani, Tehran’s chief negotiator, raised the stakes, saying that Iran had a “God- given right” to a nuclear programme. He even said that oil production might be used as a weapon if the crisis deepened.

Iran has already resumed enrichment on a small scale at its Natanz research facility, testing 20 centrifuges, according to the IAEA. Thousands of centrifuges are required to produce enough enriched uranium for a weapons programme.

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