Democrats have called for a full investigation into the use of intelligence about Iraqi weapons by the United States administration.
Bush made the uranium claim in his State of the Union address
On Tuesday the White House acknowledged that allegations that Iraq had tried to buy uranium from the African state of Niger were based on forged documents.
But in a press conference in South Africa on Wednesday, Mr Bush brushed aside a question about whether he believed the allegations were accurate when he highlighted them in January.
He said he was convinced that Saddam Hussein had posed a threat to world peace and that weapons of mass destruction would be found.
"There is no doubt in my mind that we were right," he said.
A CIA official, however, told the BBC that a former US diplomat had established in March 2002 that Iraq was not trying to obtain uranium from Niger.
And, he added, that information had been passed on to the White House well before President Bush mentioned it in his State of the Union address.
Limited reviews of intelligence material about Iraq available in the run-up to the war are under way in both houses of Congress - but senior Democrats called for a broader inquiry following the White House's admission.
"It ought to be the subject of careful scrutiny... with regard to what (President Bush) knew, what actions were taken, what statements were correct and which ones were incorrect," Senate Minority Leader Tom Daschle said on Tuesday.
Carl Levin, the senior Democrat on the Senate Armed Services Committee, said the acknowledgement only reinforced "the importance of an inquiry into why the information about the bogus uranium sales didn't reach the policymakers during 2002".
The senior Democrat on the Senate Select Committee on Intelligence, John D Rockefeller, said he was not surprised the White House had been forced to admit the uranium allegations were false.
"The whole world knew it was a fraud," he said, adding that his committee should determine how the report found its way into the State of Union speech.
Congressman Dick Gephardt - who is seeking the Democratic nomination for the presidency in 2004 - also called for a wider investigation.
"President Bush's factual lapse in his State of the Union address cannot be simply dismissed as an intelligence failure," he said.
However Republicans defended the White House's decision to admit to the mistake over the uranium allegations.
Senator Rick Santorum praised the administration for being forthright.
"I think they had the best information that they thought," he told reporters. "It has since turned out to be, at least according to one report, not true. The president stepped forward and said so."
House majority leader Tom DeLay also defended Mr Bush, saying it was "very easy to pick one little flaw here and one little flaw there" but that the overall case for the war against Iraq was "morally sound".
In his keynote speech to Congress in January, the President said: "The British Government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa."
The claim - based on British intelligence - that Iraq was trying to get uranium from Niger as part of its attempt to build nuclear weapons was also mentioned by UK Prime Minister Tony Blair.
But the documents alleging a transaction were found to have been forged.
Mr Blair is under fire from British MPs about the credibility of evidence that set out his case for war.