US Secretary of State Colin Powell told an interviewer he may not have pushed for an invasion of Iraq if he knew that it had no stockpile of banned weapons.
Last year Mr Powell tried to convince the UN Security Council Iraq had weapons
He told the Washington Post that his belief that Iraq possessed prohibited weapons was the "last little piece" that swayed him.
But Mr Powell later gave a staunch defence of President George W Bush's decision to go to war.
President Bush has ordered an inquiry into the accuracy of the intelligence.
The bipartisan US commission to be appointed to conduct the inquiry is not expected to report back before the presidential election in November, although members of the Democratic Party think it should.
On Tuesday the UK Government said it would hold its own inquiry.
'Solid evidence' questioned
As the US' top diplomat, Mr Powell had a key role in trying to gather international support for the Bush administration's decision to go to war.
Nearly one year ago he put the US case to the United Nations Security Council, saying he was offering "facts and conclusions based on solid evidence".
White House officials now concede that the intelligence may have been wrong.
Mr Powell told the newspaper that although former Iraqi leader Saddam Hussein may not have possessed chemical, biological or nuclear weapons he intended to acquire them and tried to maintain the capability of producing them in case sanctions were lifted.
But he said the belief that Iraq had these weapons had made the case for war stronger and added that he did not know if he would have recommended an invasion if this belief had proved unfounded.
"It was the stockpile that presented the final little piece that made it more of a real and present danger and threat to the region and to the world," he said.
"[The] absence of a stockpile changes the political calculus; it changes the answer you get."
But on Tuesday Mr Powell appeared to detract from such doubts, when he defended the decision to go to war in front of reporters.
"I think it was clear that this was a regime with intent,
capability and it was a risk the president felt strongly we
could not take and it was something we all agreed to and would probably agree to it again under any other set of
circumstances," he said, according to Reuters.
He said that, despite the inquiry into intelligence failures, "the bottom line is this: The president made the right
"He made the right decision based on the history of
this regime, the intention that this leader - terrible,
despotic leader - had, and the capabilities at a variety of
levels - the delivery systems that were there, and there's
nobody debating that, the infrastructure that was there, the
technical know-how that was there," he said.