A split has opened up between Britain and the United States over a claim that Iraq sought to buy uranium from the West African state of Niger.
Soldiers are yet to find weapons of mass destruction in Iraq
The White House has acknowledged for the first time that the claim might be wrong and that President Bush should not have referred to it in his State of the Union speech in January.
But UK Prime Minister Tony Blair has defended the assessment, telling a committee of MPs on Tuesday that it was not a "fantasy" and that the intelligence services themselves stood by the allegation.
The Washington Post quoted White House officials as saying, in a statement authorised by the White House: "Knowing all that we know now, the reference to Iraq's attempt to acquire uranium from Africa should not have been included in the State of the Union speech."
In the speech, President Bush had said: "The British Government has learned that Saddam Hussein recently sought significant quantities of uranium from Africa."
The reference to Iraq's attempt to acquire uranium from Africa should not have been included in the State of the Union speech
The allegation was originally contained in the British Government dossier on Iraq's alleged weapons of mass destruction, though not in one issued by the CIA.
It was one of the most significant paragraphs, since Iraq had no civilian nuclear programme and an attempt to acquire uranium indicated that it was trying to make a nuclear bomb.
The claim was undermined by the International Atomic Energy Agency which said that it was based on forged documents.
But the Foreign Office in London has always refused to accept that the allegation was wrong.
As recently as 29 June, it issued a statement saying the British information was not based on the forgeries but on other sources.
Mr Blair repeated that line in his evidence to MPs, saying it was based on "separate intelligence."
He pointed out that Iraq had imported 200 tonnes of uranium from Niger in the 1980s.
On Monday, the UK House of Commons Foreign Affairs committee asked the government to explain what the "separate intelligence" was, but the prime minister did not elaborate.
American doubts about the Niger link have existed for some time.
A former US diplomat, Joseph Wilson, was sent to Niger last year and concluded that there was probably no link with Iraq.
It is not clear if his assessment ever reached the White House.