The whistle-blower website WikiLeaks was reportedly hours away from releasing millions of confidential US diplomatic cables on Sunday as governments braced for the potential fallout.
Top US officials have raced to contain the damage in recent days by warning foreign ministries in more than a dozen countries, including key allies Australia, Britain, Canada, Israel and Turkey.
US diplomats worked through the Thanksgiving holiday weekend hoping to stave off anger over the cables, which are internal messages that often lack the niceties diplomats voice in public.
An independent French website reported that the leaks would be published simultaneously at 2130 GMT Sunday by several Western newspapers.
The website, owni.fr, had previously launched an interface allowing the public to search the Iraq war logs published by WikiLeaks in October.
It said the New York Times, Britain's The Guardian, Germany's Der Spiegel, Spain's El Pais and France's Le Monde would release their first analysis of the documents late Sunday, with leaks expected to trickle out before then.
The website said Der Spiegel had published the number of documents online Saturday for a few minutes before removing them, saying the release would include 251,287 diplomatic cables, including 16,652 marked "secret."
WikiLeaks has not specified the documents' contents or when they would be put online, but a Pentagon spokesman said officials were expecting a release early this week.
The website has said there would be "seven times" as many secret documents as the 400,000 Iraq war logs released last month.
The top US military commander, Admiral Mike Mullen, urged WikiLeaks to stop its "extremely dangerous" release of documents, according to a transcript of a CNN interview set to air Sunday.
Secretary of State Hillary Clinton has meanwhile contacted leaders in Germany, France, Saudi Arabia, the United Arab Emirates and Afghanistan over the issue, he said.
Officials in Russia, Denmark, Iceland, Norway and Sweden said they had been also been contacted by US diplomats regarding the release.
In London, the government urged British newspaper editors to "bear in mind" the national security implications of publishing any of the files.
British officials said some information may be subject to voluntary agreements between the government and the media to withhold sensitive data governing military operations and the intelligence services.
Russia's respected Kommersant newspaper said the documents included US diplomats' conversations with Russian politicians and "unflattering" assessments of some of them.
Turkish media said they include papers suggesting that Ankara helped Al-Qaeda militants in Iraq and that the United States helped Iraq-based Kurdish rebels fighting against Turkey -- potentially explosive revelations for the two allies.
The US embassy "gave us information on the issue, just as other countries have been informed," a senior diplomat in Ankara told AFP.
Foreign Minister Ahmet Davutoglu, who traveled to Washington on Saturday for previously scheduled talks with Clinton, said Turkey did not know what the documents contained.
Australia on Saturday condemned the whistle-blower website, saying the "reckless" disclosure could endanger individuals named in the documents as well as the national security interests of the United States and its allies.
US officials have not confirmed the source of the leaked documents, but suspicion has fallen on Bradley Manning, a former army intelligence agent.
He was arrested after the earlier release of a video showing air strikes that killed civilian reporters in Baghdad.
WikiLeaks argues that the first two document dumps -- US military incident reports from 2004 to 2009 -- shed light on the wars in Afghanistan and Iraq, including allegations of torture by Iraqi forces and reports that suggested 15,000 additional civilian deaths in Iraq.
WikiLeaks is the project of Australian hacker Julian Assange. Sweden recently issued an international warrant for his arrest, saying he is wanted for questioning over allegations of rape and sexual molestation.