The Pentagon has assembled a 120-member team to prepare for the expected publication of some 400,000 Iraq war documents on the Wikileaks website.
The documents are thought to concern battle activity, Iraqi security forces and civilian casualties.
Colonel Dave Lapan, a Pentagon spokesman, said the timing of the leak remained unclear but are preparing for it to be as early as Monday or Tuesday - a possibility raised in previous WikiLeaks statements.
The Pentagon said on Sunday it wants the documents back to avoid "potentially damaging" information being released.
Lapan said the files were from an Iraq-based database that contained "significant acts, unit-level reporting, tactical reports, things of that nature".
If confirmed, the leak would be much larger than the record-breaking release of more than 70,000 Afghan war documents in July, which stoked debate about the nine-year-old conflict but did not contain major revelations.
Spencer Ackerman, a journalist who has covered Wikileaks extensively, told Al Jazeera this particular release of documents would dwarf Wikileaks' July publication of more than 70,000 Afghan war files.
"The Pentagon recently assessed that the initial impact of the Afghanistan document release was not as great as they had feared. This time, however, Wikileaks is talking about releasing in the neighbourhood of 400,000 documents as opposed to the 92,000 they obtained from Afghanistan - it may in fact be very significant," he said.
"A history of the Iraq war that no one has ever seen, from 2004 to 2009, will be out in the public domain."
According to Ackerman, the documents are expected to include "a lot of frontline military reports about how US troops perceived the war".
"We may learn a fair amount about civilian casualties, the birth of the improvised explosive device - the signature weapon of this war and we may learn a lot about the nature of the insurgency contrary to what some statements from top US officials said back then."
The document release could renew debate about foreign and domestic actors influencing Iraq, which has been wrestling with a political vacuum since an inconclusive election in March.
Lapan said the Pentagon team believed it knew which documents WikiLeaks may be releasing since it had already reviewed the Iraq war file. That could speed up its assessment about potential fallout.
The largest security breach
At the time of the Afghan war leak, US military officials warned that the whistleblower website might cause the deaths of US soldiers and Afghan civilians because some of the documents contained the names of locals who had helped coalition forces.
It was the largest security breach of its kind in US military history.
There have been fears that such leaks could damage US intelligence sharing with other nations as well as intelligence sharing between US agencies.
The investigation into the Afghan leak has focused on Bradley Manning, a US army intelligence analyst who is in custody and has been charged with leaking a classified video of a US helicopter attack in Iraq in 2007 in which a dozen people were killed.
The Wikileaks website is currently offline "undergoing scheduled maintenance". Julian Assange, the founder of Wikileaks, is being investigated in Sweden over an alleged sex crime.
He denies the charge and says the allegations are part of a smear campaign by opponents of his whistle-blowing website.
WikiLeaks says it is a non-profit organisation funded by human rights campaigners, journalists and the general public. But the Pentagon has demanded it return classified information and critics have questioned its perceived anti-war agenda.