Aides told journalists three hours before a speech on Friday that Blair would stress that "change should not be imposed" on Iran, reflecting Britain's view that bombing or invading Iran is unrealistic, The Sunday Telegraph said.

US officials had insisted, however, that the possibility of military action remained "on the table", as it helped to exert maximum pressure on President Mahmoud Ahmadinejad, according to the report based on unnamed British sources.

By the time he made his key speech on foreign policy at Georgetown University, Blair said only that "I am not saying we should impose change," leaving the door open for military strikes.

Blair meanwhile backed down from plans to take a tough line on global warming and the Kyoto Treaty, which Washington still has not signed, the newspaper said.

In the end, Blair merely claimed: "We must act on climate change", but did not go into detail.

At this point, as a mobile telephone rang in the audience, Blair even made a joke about US interference, the newspaper said. "I hope that isn't the White House telling me they don't agree with that. They act very quickly, these guys."

The newspaper said the prime minister also backed away from a planned demand for a change in the running of the world's biggest financial institutions, the International Monetary Fund and the World Bank.

Blair had intended to outline a plan for Europe and the United States to give up their exclusive rights to appoint their own nationals as heads of the bank and the IMF respectively, the Telegraph said.

Such a move would help to persuade smaller nations to give up their effective right to choose the United Nations secretary general and allow for a a leading international figure, it said.

Instead, Blair's speech simply cited a "powerful case for reform."

However, a spokesman in Blair's office at 10 Downing Street denied the Telegraph report.

"That is absolutely untrue," the spokesman said. "I categorically deny that objections by the White House played any part in the prime minister's speech whatsoever."

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