The statement, made by Donald Rumsfeld, the US Defence Secretary, came amid growing anger on Capitol Hill about prewar intelligence.

It followed a White House admission on Monday that President Bush used bogus evidence when he claimed in the State of the Union address in January that Iraq had tried to buy uranium from Africa. The rapidly gathering political storm in Washington threatened to overshadow Mr Bush’s five-nation African tour. Mr Bush was forced to defend himself and his Administration over the use of prewar intelligence at a press conference in Pretoria with President Mbeki of South Africa.

Mr Rumsfeld, testifying before the Senate Armed Services Committee, said that the US-led coalition “did not act in Iraq because we had discovered dramatic new evidence of Iraq’s pursuit of weapons of mass murder”. Rather, he said, the United States acted because the Administration saw “existing evidence in a new light, through the prism of our experience on September 11”.

That claim appeared to shift significantly from the Administration’s stance before the war, most notably from assertions made by Colin Powell, the Secretary of State, in an address to the UN Security Council in February. One of the key points of General Powell’s address, which was the Administration’s detailed case against Saddam, was new evidence “to show that Saddam Hussein and his regime are concealing their efforts to produce more weapons of mass destruction”.

General Powell cited reports less than five months old showing the dispersal of missiles armed with biological warheads, and “recent” satellite photographspurportedly showing the removal of chemical weapons.He cited intelligence from “the past 18 months” that he said proved Saddam was reactivating his nuclear weapons programme.

In the week before the war, Dick Cheney, the Vice-President, said: “We know he’s out trying once again to produce nuclear weapons”. In October, Mr Bush said that Saddam was an imminent threat because of his past “and present” actions.

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