The Obama administration has alerted Congress and foreign governments ahead of the expected release of more sensitive documents on the WikiLeaks website.
They fear the release of US diplomatic files could damage relations with friends and allies across the globe.
“These revelations are harmful to the US and our interests,” said State Department spokesman PJ Crowley. “They are going to create tension in relationships between our diplomats and our friends around the world.”
Mr Crowley said the release of confidential communications about foreign governments will probably erode trust in the US as a diplomatic partner and could cause embarrassment if the files should include derogatory or critical comments about friendly foreign leaders.
“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,” Crowley said.
US diplomatic outposts around the world have begun notifying other governments that WikiLeaks may release these documents in the coming days, Crowley said.
A major focus of the documents is Europe but the cables are likely to touch on relations with many important countries in Asia and elsewhere, another official said. The release is expected to happen this weekend, although WikiLeaks has not been specific about the timing.
In two previous releases of leaked secret US government documents, in July and October, WikiLeaks provided them in advance to The New York Times, the Guardian and the German magazine Der Spiegel on condition that they publish their stories simultaneously.
The first leak contained thousands of military field reports on the war in Afghanistan; the second was a similar but larger file on the Iraq war.
A statement on WikiLeaks Twitter site said: “The Pentagon is hyperventilating again over fears of being held to account.”