The United States has briefed several foreign governments, about the likely release of diplomatic files by whistleblower site Wikileaks.
The top US military commander Admiral Mike Mullen said the release of diplomatic cables was "extremely dangerous" and could put lives at risk.
Wikileaks has said the US authorities are afraid of being held to account.
It has not confirmed exactly when the documents will be made public.
The website, founded by Australian Julian Assange, said earlier this week that the release would be nearly seven times larger than the nearly 400,000 Pentagon documents related to the Iraq war it published in October.
Analysts say the US and its allies have the potential to be embarrassed by the publication of candid assessments of foreign governments by its officials, the BBC reports.
State department spokesperson PJ Crowley warned that the release could weaken trust in the US as a diplomatic partner.
"When this confidence is betrayed and ends up on the front pages of newspapers or lead stories on television or radio, it has an impact," he said.
Newspaper reports indicate the release will include papers suggesting that Turkey helped al-Qaeda militants in Iraq, and that the US helped Iraq-based Kurdish separatists who have been engaged in a long conflict with Turkey.
Washington's ambassador to Iraq, James Jeffrey, is quoted by AFP news agency as saying Wikileaks is an "absolutely awful impediment" to US efforts to build trust with other nations.
The source of the documents potentially involved in the latest Wikileaks release is not known.
However, US Army Private Bradley Manning, a military analyst who was arrested in June on suspicion of leaking classified data, is currently in custody awaiting trial.
He is alleged to have abused access to a secret-level network to obtain tens of thousands of US state department cables, some of them classified.