His statement seemed likely to add to an embarrassing rift between London and Washington -- allies in the war to overthrow Saddam Hussein (news - web sites) -- over the way intelligence was used in the run-up to the conflict.
The issue could cloud talks in Washington on Thursday when British Prime Minister Tony Blair (news - web sites) meets with President George W. Bush (news - web sites) and makes a special address to Congress.
Straw, speaking on BBC radio, stood by Britain's claim, which was contained in a controversial 50-page dossier on Saddam's pursuit of nuclear, biological and chemical weapons issued last September.
"We believe in the intelligence which was behind the claims made in the September 24 dossier, yes," he said on the Today current affairs program when asked if the intelligence on Niger was still valid in the eyes of the British government.
He added, however, that Britain was not at liberty to tell the United States where it got the information, because it had come from "foreign intelligence sources".
"It just happens to be the rules of liaison with foreign intelligence sources that they own the intelligence. The second intelligence service does not and therefore is not able to pass it on to the third party."
France and Italy both issued swift denials that their intelligence services were the origins of the contested claim about Niger.
In Rome on Sunday, the government reacted to a report in the Corriere della Sera daily that it had tipped off US and British officials back in 2001 to Iraq's quest.
France on Monday also slapped down a report in Britain's Financial Times newspaper that fingered both it and Italy.
"Contrary to the insinuations which appeared in the British press, France is not behind the intelligence published in the British dossier dated September 24, 2002 and relative to the nuclear program of Iraq," the French foreign ministry said in a statement.
The Financial Times reported Monday that "two foreign governments, thought to be France and Italy", had informed Britain that Iraq was seeking uranium from Niger -- and that therefore the September dossier had kept the allegation, despite the CIA (news - web sites) expressing "reservations" about it.
Bush, in his State of the Union address last January when he made his case for war on Iraq, included the reference to Niger, attributing it to British intelligence.
But last Saturday, CIA director George Tenet cast doubt on the accuracy of the claim, saying it should never have been included in Bush's speech.
Blair was Bush's staunchest ally on Iraq, but since combat was declared over on May 1 US and British forces have yet to unearth hard proof of Saddam's weapons of mass destruction -- let alone the man himself.
On Monday Blair said Britons should be "proud" of having helped the United States overthrow Saddam's regime in Iraq.
"When we have over the past couple of days taken the first steps for Iraqi people actually to take control of their own lives, and we have the United Nations (news - web sites) talking about 300,000 people and mass graves, then I believe we should be proud that Saddam has gone, glad that he has gone," he said.
"I have no doubt at all that in the future, whatever the differences have been in the past, we can reconstruct Iraq as a stable and prosperous country and the world will be a more secure place as a result," Blair told a gathering of fellow center-left world leaders.
"We should be proud as a country of what we have done."
