The U.S. administration has abruptly revised its explanation for invading Iraq, as Defence Secretary Donald Rumsfeld asserted that a changed perspective after the Sept. 11 terrorist attacks — not fresh evidence of banned weapons — provoked the war.

"The coalition did not act in Iraq because we had discovered dramatic new evidence of Iraq's pursuit of weapons of mass murder," Mr. Rumsfeld testified yesterday before the Senate armed services committee.

"We acted because we saw the evidence in a dramatic new light, through the prism of our experience on 9/11."

It was an about-face from a man who confidently proclaimed in January: "There's no doubt in my mind but that they [the Iraqi government] currently have chemical and biological weapons." (He was seconded in March by Vice-President Dick Cheney, who said of former Iraqi dictator Saddam Hussein: "We believe he has, in fact, reconstituted nuclear weapons.")

And in London Thursday, the BBC reported senior British government sources saying that Whitehall had virtually ruled out finding weapons of mass destruction in Iraq, which they now believe were destroyed or hidden permanently before the war began.

Mr. Rumsfeld's reversal came as the administration scrambled to defend itself from accusations that it deliberately used false or misleading information to bolster one of its primary justifications for the war.

On Monday, the White House acknowledged that U.S. President George W. Bush was wrong when he said in his State of the Union address in January that Iraq had recently tried to purchase large quantities of uranium from Africa to build nuclear weapons. He cited British intelligence reports of documents that purported to show an Iraqi attempt to buy a form of raw uranium known as yellowcake. The documents were later discredited as forgeries.

While the White House justified the invasion to topple Mr. Hussein on the ground that his biological, chemical and nuclear weapons posed a threat, no such arms have been uncovered in the 10 weeks since the war ended.

Mr. Bush unapologetically defended the war while in the middle of his five-day, visit to Africa.

"Saddam Hussein was a threat to world peace. And there's no doubt in my mind that the United States, along with allies and friends, did the right thing in removing him from power," he said yesterday at a joint news conference with South African President Thabo Mbeki.

Questioned for the first time about the uranium, he said: "There's going to be a lot of attempts to rewrite history. But I am absolutely confident in the decision I made."

White House officials said information that the documents may have been forged had not reached top-level policymakers before the public statements.

Mr. Rumsfeld said he found out "within recent days" that the information had been discredited, but he defended the U.S. intelligence throughout the Iraq conflict as "quite good" and said Iraq "had 12 years to conceal" weapons programs. "Uncovering those programs will take time," he said.

Several Democrats heightened calls for a full-scale investigation on whether intelligence was manipulated.

"It's bad enough that such a glaring blunder became part of the President's case for war," Senator Edward Kennedy said. "It's far worse if the case for war was made by deliberate deception. ... We cannot risk American lives based on shoddy intelligence or outright lies."

With U.S. and British forces facing almost daily assaults, he and other senators grilled Mr. Rumsfeld on whether more troops were needed in Iraq.

Mr. Rumsfeld told the committee that talks were under way to increase NATO involvement in Iraq peacekeeping efforts. He maintained that most of Iraq is safe after the war, with most of the recent attacks against U.S. and British forces concentrated in Baghdad and surrounding areas.

Mr. Kennedy expressed skepticism, saying he was "concerned that we have the world's best-trained soldiers serving as policemen in what seems to be a shooting gallery."

With reports from the Guardian, Reuters