President Ahmadinejad vowed yesterday to resist pressure from “bullies and corrupt powers” on Iran to abandon its nuclear programme, which he described as a potential “role model” for other countries.

The Iranian leader’s comments, delivered to a crowd in the northern town of Fuman, came 24 hours after the United Nations’ nuclear watchdog reported that Tehran had not only failed to halt uranium enrichment but was expanding its activities.

Iran insists that its programme is peaceful, but the United States and other Western countries believe that it is a cover to develop weapons.

Diplomats from the five permanent UN Security Council members and Germany will meet in London on Monday to discuss further measures designed to end Iran’s defiance. Last year the Security Council introduced limited economic sanctions and gave Iran 60 days to comply — a deadline that expired on Wednesday.

There are emerging differences on how to tackle Iran, with divisions opening up inside the US Administration and between America and Britain. Tony Blair stated publicly this week that a military attack on Iran would be wrong and that diplomacy was the “only way” to get a sensible solution.

Although this view chimes with that of many senior figures in the Bush Administration, including Robert Gates, the Defence Secretary, it prompted a swift and uncompromising response from Dick Cheney, the Vice-President.

In an interview with ABC yesterday, Mr Cheney — who is regarded as the Administration’s leading hawk — made plain that military action was still possible, saying repeatedly that “we haven’t taken any options off the table”. Iran had “defied the United Nations”, he added, “and now we’ll have to see whether or not the international community is really serious about insisting on them giving up their nuclear aspirations”.

Mr Cheney’s apparent impatience with the diplomatic process reflects disagreement, even between the US and Britain, on exactly what measures should be taken by the Security Council against Iran.

One diplomatic source said yesterday: “We both want to go as far as possible but there are tactical judgments about the extent to which we can persuade other members — such as Russia or China — to come with us and not veto any new resolution.”

There is growing unease in Washington over recent signs of Britain breaking ranks with President Bush. Nile Gardiner, of the conservative think-tank Heritage Foundation, said that Mr Blair’s comments were “sending the wrong signals” to Tehran “at a critical time and represented a significant weakening of his position”.

He suggested that the Prime Minister was no longer the dependable ally, and that it may be Gordon Brown who was beginning to “call the shots” in foreign policy. Downing Street denied yesterday that there was any “internal political agenda” behind Mr Blair’s comments on Iran or his decision this week to begin withdrawing troops from Iraq — the timing of which is known to have displeased the White House.

Other leading conservative voices in Washington, such as Danielle Pletka, of the American Enterprise Institute, said that it was dangerous to “overinterpret” recent events.

“Tony Blair has put a huge amount into this relationship and it has been very difficult for him. When he pulls a few troops home, is that a slap in the face for us? Or is it just good sense?” she asked.

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