The CIA called into question UK claims in last September's dossier that Saddam Hussein was buying in uranium from Africa even before the document was published, it has been confirmed.
The search for weapons of mass destruction goes on in Iraq
The Foreign Office in London - which made the admission - also said that, despite US concerns, Britain decided to go ahead and publish the claims because they believed their intelligence to be reliable.
A decision was therefore taken not to include the doubts expressed by America.
The news comes in the latest report by the Commons foreign affairs committee which has been investigating the way the government's case for war with Iraq was presented.
The MPs had asked Foreign Secretary Jack Straw to answer nine questions about the alleged supply of uranium by the African state Niger.
Responding, the Foreign Office said that it saw no need to include a "health warning" about the African element of the dossier - even though the CIA did not find it credible.
In a statement the Foreign office repeated a past assertion that "the reference in the dossier was based on intelligence from more than one source."
But foreign affairs committee chairman, Labour MP Donald Anderson, said he believed it would have been "prudent" for the government to have included the CIA's concerns in September's dossier.
And he complained that the answers to the committee's questions were not as full as the MPs would have liked.
Despite US scepticism, President George W Bush referred to the uranium claims in his State of the Union speech in January.
Since then 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 UK claims were highly significant 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.
Iraq is believed to have imported 200 tonnes of uranium from Niger in the 1980s.