The WikiLeaks website has promised a "major announcement" in Europe on Saturday, in a message on its Twitter feed, amid speculation it will release thousands of secret documents about the Iraq war.
"Major WikiLeaks announcement in Europe at 10am tomorrow," said the message posted Friday, appearing to confirm the site is preparing to leak what the US military and NATO fear will be tens of thousands of classified military papers.
The Pentagon warned Friday that releasing secret military documents could endanger US troops and Iraqi civilians.
WikiLeaks infuriated the Pentagon in July by publishing 77,000 classified US military documents on the war in Afghanistan.
Speaking Friday, Pentagon press secretary Geoff Morrell said: "By disclosing such sensitive information, WikiLeaks continues to put at risk the lives of our troops, their coalition partners and those Iraqis and Afghans working with us."
He said the documents were "essentially snapshots of events, both tragic and mundane, and do not tell the whole story".
"That said, the period covered by these reports has been well-chronicled in news stories, books and films and the release of these field reports does not bring new understanding to Iraq's past," Morrell added.
The Pentagon has identified what it believed were roughly 400,000 documents that WikiLeaks was likely to release, after it was contacted by media who had been given the files by the website, another spokesman told reporters.
The documents are based on reports from military units that convey "raw" intelligence, but do not shed new light on a war that has been thoroughly documented, Colonel Dave Lapan said.
NATO chief Anders Fogh Rasmussen also said Friday that the lives of soldiers and civilians could be placed in peril if WikiLeaks released confidential documents.
"Such leaks are very unfortunate and may have very negative security implications for people concerned," Rasmussen said at a press conference with German Chancellor Angela Merkel in Berlin.
"Leaks may put soldiers as well as civilians at risk," he added.
The Pentagon said last week a 120-strong taskforce was scouring an Iraq war database to prepare for the potential fallout from the release of secret military reports.
It appealed to the media to avoid facilitating the leak of documents regarding Iraq.
In July, WikiLeaks published 77,000 classified US military documents on the war in Afghanistan and is expected to publish another 15,000.
The documents on Afghanistan, revealing details of civilian victims and supposed links between Pakistan and the Taliban insurgents, enraged the Pentagon.
Human rights groups were also worried that the names of Afghans aiding US forces had not been erased, potentially leaving them open to reprisals.
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