The CIA warned the US Government that claims about Iraq's nuclear ambitions were not true months before President Bush used them to make his case for war, the BBC has learned.
Soldiers are yet to find weapons of mass destruction in Iraq
Doubts about a claim that Iraq had tried to buy uranium from the African state of Niger were aired 10 months before Mr Bush included the allegation in his key State of the Union address this year, a CIA official has told the BBC.
On Tuesday, the White House for the first time officially acknowledged that the Niger claim was wrong and suggested it should not have been used in the president's State of the Union speech in January.
But the CIA official has said that a former US diplomat had already established the claim was false in March 2002 - and that the information had been passed on to government departments, including the White House, well before Mr Bush mentioned it in the speech.
Both President Bush and UK Prime Minister Tony Blair mentioned the claim, based on British intelligence, that Iraq was trying to get uranium from Niger as part of its attempt to build a nuclear weapons programme.
Mr Blair is under fire from British MPs about the credibility of a dossier of evidence, which set out his case for war.
And in the US, increasing doubts are being raised about the American use of intelligence.
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."
But the documents alleging a transaction were found to have been forged.
White House spokesman Ari Fleischer appeared to concede on Tuesday that the uranium claim in the State of the Union address was based on inaccurate information.
"The president's statement was based on the predicate of the yellow cake [uranium] from Niger," Mr Fleischer said.
"So given the fact that the report on the yellow cake did not turn out to be accurate, that is reflective of the president's broader statement."
But a former US diplomat, Ambassador Joseph Wilson, went on the record at the weekend to say that he had travelled to Africa to investigate the uranium claims and found no evidence to support them.
Now the CIA official has told the BBC that Mr Wilson's findings had been passed onto the White House as early as March 2002.
That means that the administration would have known nearly a year before the State of the Union address that the information was likely false.
In response, a US Government official told the BBC that the White House received hundreds of intelligence reports every day.
The official said there was no evidence that this specific cable about uranium had been passed on to the president.
But in Congress, Democrats are demanding a full investigation into the intelligence that underpinned the case for war.
They have demanded to know if President Bush used evidence that he knew to be weak or wrong.
The British Government has stood by its assertion, saying the forged documents were not the only evidence used to reach its conclusion that Saddam Hussein tried to buy uranium from Africa.
On Tuesday Mr Blair defended the assessment, telling a committee of MPs that it was not a "fantasy" and that the intelligence services themselves stood by the allegation.
"The evidence that we had that the Iraqi Government had gone back to try to purchase further amounts of uranium from Niger did not come from these so-called 'forged' documents, they came from separate intelligence," Mr Blair said.
However, Mr Blair did not specify what that separate intelligence was.