Top officials from the United States, Australia and Great Britain stood firmly behind the case for war, in remarks from Rome, Malaysia and the Group of Eight summit here.
"I stand absolutely, 100 percent behind the evidence, based on intelligence, that we presented people," Blair said during a news conference on the sidelines of the G-8.
Accusations that his government had manipulated evidence were "completely and totally false," Blair said.
A former member of Blair's Cabinet claimed in a newspaper interview published Sunday that the prime minister had spun intelligence on Iraqi weapons to win support for the war.
"I have concluded that the prime minister had decided to go to war in August sometime and he duped us all along," Clare Short, who resigned as international development secretary last month in protest at Blair's Iraq policy, was quoted as saying in The Sunday Telegraph newspaper.
Blair and President Bush insisted in the run-up to the war that the existence of evidence of a powerful arsenal of weapons of mass destruction in Iraq justified military action against Saddam Hussein.
But the failure of American and British troops so far to uncover new evidence that Saddam had banned weapons is creating a political problem for Blair in Britain that threatens to undermine his international credibility.
The G-8 is primarily about economic issues, but Iraq and the dispute that preceded the war loomed large here.
In Rome, Secretary of State Colin Powell gave a lengthy defense of the case the United States made on Iraq's weapons. "There were weapons of mass destruction in Iraq. It wasn't a figment of anyone's imagination," he said Monday at a news conference with Italian Foreign Minister Franco Frattini.
"What we have to do now is not get trapped in the long-winded debate about what was known and not known," he said.
"It's not a question of admitting we were wrong or saying that there wasn't the evidence, because the evidence was there," British Foreign Secretary Jack Straw told British Broadcasting Corp. radio. "The evidence is overwhelming."
Straw cited a report by chief U.N. weapons inspector Hans Blix last March that cited outstanding disarmament tasks yet to be carried out by the Iraqis — although inspectors also said they found no chemical, biological or nuclear weapons in 3½ months of searching.
The most significant finds reported by inspectors were a dozen artillery shells filled with mustard gas and fewer than 20 empty chemical warheads for battlefield rockets.
"I've got in front of me the 173 pages of the unanswered disarmament questions which Dr. Blix put before the Security Council," Straw said. "Our point is this: Look, if Saddam had nothing to hide why had he failed over a 12-year period to provide answers to these questions?"
At a news conference in Penang, Malaysia, the defense ministers from Britain and Australia said intelligence pointing to illicit weapons in Iraq justified the invasion.
British Defense Minister Geoffrey Hoon said "We've made clear that we stand by our belief that weapons of mass destruction are there and we continue to make determined efforts to identify them."
He pointed to two vehicles found recently in Iraq that are being investigated as possible mobile biological weapons laboratories.
The two vehicles "can only be used for the production of biological weapons," he said, adding: "I'm not sure how much stronger evidence you require of a capability to produce some of the world's most appalling weapons."
Australian Defense Minister Robert Hill said there was a "mass of evidence" about Saddam's weapons of mass destruction that was "publicly acknowledged across the world."
But he conceded to some holes in the coalition's intelligence.
"What we didn't know was the full extent to which the weapons program had been further developed; we didn't know the full extent to which some may have been dismantled, and we will establish that full picture in the full course of time," Hill said.
The news conference followed biennial talks on a defense agreement between Britain and four of its former colonies — Australia, Malaysia, New Zealand and Singapore.