Secretary of State Condoleezza Rice said the director of national intelligence, John Negroponte, was combing thought the Arabic-language material "to see whether or not there were documents there that are particularly troubling".
Rice confirmed that the Pentagon website set up last March to make documents found in Iraq following the ouster of Saddam Hussein available to the public, had been "taken down" after concerns were raised about its content.
The New York Times reported on Friday that officials from the International Atomic Energy Agency had complained to Washington last week about the postings of "roughly a dozen" documents from Iraq's pre-1991 nuclear research that contained diagrams, equations and other details for making a nuclear bomb.
One of the documents, running to 51 pages, covered the technical advances of Iraq's early nuclear program, including 18 pages on the development of its bomb design -- materials that one expert told the Times "constitute a basic guide to building an atom bomb."
In a radio interview on Friday Rice defended the original posting of the captured Iraqi archives.
"But obviously we want to be in a position of protecting anything that might give an upper hand to people trying to build weapons of mass destruction, and so the DNI, John Negroponte, is taking a look at it and I'm certain it will be taken care of," she said.
The US government created the website, called the Operation Iraqi Freedom Document Portal, in March to make available to the public a huge archive of Iraqi government papers in the hope that private experts might find useful information government translators did not have time to locate.
The Times said that earlier in the year UN arms control officials had complained about documents on the website that had information on producing the extremely dangerous nerve agents sarin and tabun.
The Department of Defence set up the Iraqi website under pressure from legislators to find a way to quickly sort through some 48,000 boxes of mostly Arabic documents seized in the 2003 invasion of Iraq.
The idea was to let the public help in reading and translating the documents, with hopes that they might shed light on matters such as deposed Iraqi leader Saddam Hussein's weapons programs.
While many of the documents have proven innocuous, the Times said the nuclear material was identical to papers presented to the UN Security Council in 2002 in the lead-up to the US invasion.
However, the documents the Security Council saw were heavily edited to mask "sensitive information on unconventional arms," the newspaper said.
It added that a senior diplomat in Europe called the documents a "cookbook" for making a bomb.
"If you had this, it would short-circuit a lot of things," the diplomat said.
Peter Zimmerman, a physicist and weapons scientist at King's College London, said the documents were "very sensitive."
But the United States appeared to have ignored warnings about dangerous documents surfacing on the website.
In June, the Times said, Demetrius Perricos, the acting chief weapons inspector of the UN Monitoring, Verification and Inspection Commission, complained to the Security Council about the appearance of risky arms information on a public website.
Nevertheless, the nuclear bomb papers were posted on the site in September.

Copyright AFP (Agence France-Presse), 2006