Annan, speaking after meeting here with Secretary of State Colin Powell, declined all substantive comment on the matter, telling reporters that the United Nations had "dropped" the matter, after the head of the UN atomic energy chief Mohamed ElBaradei said in March that the claims were false.

"As you know this was an issue discussed in the Security Council and the head of the atomic agency, ElBaradei, at that time indicated that the documentation was fraudulent and I think the council dropped it there and we didn't take it any further," he said.

Annan referred to ElBaradei's comments to the UN Security Council in March in which he said documents purporting to show that Iraq had sought to buy uranium "yellowcake" from Niger had been falsified as the debate over US plans for a war with Iraq intensified.

Annan also refused to say whether he would now question other US intelligence reports about ousted Iraqi leader Saddam Hussein's alleged procurement of weapons of mass destruction.

"I would say that there are discussions going on now in the government, the leaders in Washington are discussing it and I will leave them to review that topic," he said.

US Central Intelligence Agency director George Tenet has taken the blame for President George W. Bush's January claim that Iraq had tried to buy nuclear material from Africa.

In a surprise statement on Friday, Tenet said the reference -- based on information from Britain -- should not have been included in the president's January 28 State of the Union address because it had not been corroborated by US intelligence.

His admission has prompted calls for his resignation but Bush and his top aides have defended the CIA chief.

Meanwhile British Foreign Secretary Jack Straw said Monday that London cannot tell Washington about the details of the Niger claim because the information originated from a third country.

The issue is liable to cloud talks here on Thursday when British Prime Minister Tony Blair -- en route to East Asia -- meets with Bush 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 chemical, biological and chemical 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 British eyes.

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," Straw said. "The second intelligence service does not and therefore is not able to pass it on to the third party."

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