Democrats pounced on the disclosure and fears the Saddam Hussein-era documents could have helped terrorists or US foe Iran to again skewer President George W. Bush over Iraq before mid-term polls on Tuesday, expected to deal Republicans heavy losses.
Intelligence officials hurriedly pulled down the federal website displaying reams of Iraqi government papers on Thursday night, following a report they included details of Baghdad's secret nuclear research prior to 1991.
The New York Times quoted experts as saying the papers added up to a basic guide on how to build a nuclear bomb, nuclear firing circuits and the radioactive cores of atom bombs.
It quoted European diplomats as saying the International Atomic Energy Agency (IAEA) had complained to the US government about the documents last week, fearing they could help states like Iran develop nuclear arms.
The Operation Iraqi Freedom Document Portal was created in March to display a huge archive of Iraqi papers, many in Arabic, in the hope private experts might find useful information.
But Democrats charged the site was merely an attempt by Republicans to hype the threat from Saddam, after the failure to find the weapons of mass destruction Bush used to justify the 2003 invasion of Iraq.
"Whoever authorised putting partisan political considerations above national security in this instance must be held accountable," said Nancy Pelosi, Democratic Party leader in the House of Representatives.
But White House counsellor Dan Bartlett played down the controversy and suggested the documents proved Saddam was actively seeking nuclear weapons, even though they dated from before 1991.
"They reveal what many people knew, that Saddam Hussein had the capability and was working toward a nuclear weapon program ... I think that's a stark reminder for people," he told MSNBC.
But Joseph Cirincione, a nuclear expert now at the left-leaning Center for American Progress, called the controversy "absolutely outrageous." "The political leadership of this country just glosses over this grievous breach of national security and the damage that has been done," he said.
Though he had not seen the documents, Cirincione said they appeared to go beyond anything currently available on the web.
"There are no diagrams up there from actual national nuclear bomb programs -- that is what we are talking about here," he said.
But a US intelligence official cast doubt on suggestions that the documents contained everything needed to make a home-made bomb.
"I am not at all confident that that is the case," the official said on condition of anonymity.
Bartlett also said that that it was open to dispute that such information was available elsewhere on the web.
The Office of the Director of National Intelligence "suspended access" to the website to ensure documents were suitable for the public, spokesman Chad Kolton said.
"The material currently on the website, as well as the procedures used to post new documents, will be carefully reviewed before the site becomes available again."
The IAEA complained last week to the US ambassador to the body about the postings of "roughly a dozen" documents that contained diagrams, equations and other details for making a nuclear bomb, the Times said.
But Peter Hoekstra, Republican chairman of the House Intelligence Committee, accused the IAEA of going to the press before it brought up the issue with the US government.
A second New York Times disclosure, over an attempt by Republicans to force the closure of the Office of the Special Inspector General for Iraq Reconstruction, touched off another political row.
The paper reported that Republican aides in the House had slipped a clause requiring the closure of the office by October 1, 2007, into a huge military spending bill signed by Bush two weeks ago.
The inspector-general, Stuart Bowen, has exposed a sheaf of embarrassing missteps of the reconstruction effort in Iraq.

Copyright AFP (Agence France-Presse), 2006