Governments around the world on Saturday braced for the release of millions of potentially embarrassing US diplomatic cables by WikiLeaks as Washington raced to contain the fallout.

The whistle-blower website is expected to put online three million leaked cables covering US dealings and confidential views of countries including Australia, Britain, Canada, Israel, Russia and Turkey.

US diplomats skipped their Thanksgiving holiday weekend and headed to foreign ministries hoping to stave off anger over the cables, which are internal messages that often lack the niceties diplomats voice in public.

"WikiLeaks are an absolutely awful impediment to my business, which is to be able to have discussions in confidence with people. I do not understand the motivation for releasing these documents," said James Jeffrey, the US ambassador to Iraq.

"They will not help, they will simply hurt our ability to do our work here," he told reporters.

The top US military commander, Admiral Mike Mullen, meanwhile urged WikiLeaks to stop its "extremely dangerous" release of documents, according to a transcript of a CNN interview set to air Sunday.

State Department spokesman Philip Crowley also condemned WikiLeaks' plans.

"It will place lives and interests at risk. It is irresponsible," he said.

Secretary of State Hillary Clinton had contacted leaders in Germany, Saudi Arabia, the United Arab Emirates, Britain, France and Afghanistan over the issue, he added.

Russia's respected Kommersant newspaper said that the documents included US diplomats' conversations with Russian politicians and "unflattering" assessments of some of them.

Russian Foreign Minister Sergei Lavrov blamed the impending file dump on "little thieves running around the Internet," the Interfax news agency quoted him as saying.

WikiLeaks has not specified the documents' contents or when they would be put online, but Pentagon spokesman Colonel Dave Lapan said officials were expecting a release "late this week or early next week."

The website has said there would be "seven times" as many secret documents as the 400,000 Iraq war logs it published last month.

Turkish media said the planned release includes 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.

Foreign Minister Ahmet Davutoglu said Turkey did not know what the documents contained.

"This is speculation," he said on CNN Turk. "But as a principle, tolerating or ignoring any terrorist action that originates in Turkey and targets a neighboring country, particularly Iraq, is out of the question."

Israel has also been warned of potential embarrassment from the latest release, which could include confidential reports from the US embassy in Tel Aviv, Haaretz newspaper said, citing a senior Israeli official.

The US ambassador in Canada telephoned Foreign Minister Lawrence Cannon about the leak, a ministry spokeswoman said, adding that the Canadian embassy in Washington was "engaging" with the State Department on the matter.

Italy's Foreign Minister Franco Frattini told parliament that US diplomats informed him "that the person responsible for leaking the information has been arrested."

The government meanwhile said that it was alarmed about "possible negative repercussions for Italy" from the release of the cables.

Officials in Australia, Britain, Denmark, Iceland, Norway and Sweden also said they had been contacted by US diplomats regarding the release.

Australia on Saturday condemned the whistle-blower website, saying the planned release could be a national security risk.

"The reckless and large-scale exposure of classified material by WikiLeaks could put at risk individuals named in these documents and harm the national security interests of the United States and its partners," an Australian foreign affairs spokesman said.

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.

Wired magazine said Manning confessed to the leaks during a webchat in May. He was quoted as saying he acted out of idealism after watching Iraqi police detain men for distributing a "scholarly critique" against corruption.

WikiLeaks argues that the first two document dumps -- US soldier-authored 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.

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