The whistleblowing website WikiLeaks was preparing to release a cache of 250,000 classified U.S. State Department documents as early as Sunday.
The State Department told website founder Julian Assange in a letter on Saturday the release would endanger countless lives, jeopardize American military operations and hurt international cooperation on global security issues.
U.S. ambassadors anticipate embarrassing revelations affecting Washington's relations with its allies and other nations.
Here are some facts about WikiLeaks:
* WikiLeaks says it is a non-profit organization funded by human rights campaigners, journalists and the general public. Launched in 2006, it promotes the leaking of information to fight government and corporate corruption.
* In October, WikiLeaks released 400,000 secret U.S. files on the Iraq war. The documents involved sensitive subjects including abuse of Iraqi prisoners in U.S. custody, Iraqi rights violations and civilian deaths.
* In July, it released tens of thousands of secret U.S. military documents about the war in Afghanistan, offering them first to The New York Times, Britain's Guardian newspaper and Germany's Der Spiegel.
* The Pentagon said the Afghan war documents leak -- one of the largest in U.S. military history -- had put U.S. troops and Afghan informers at risk.
* Under the heading "Afghan War Diary," the 91,000 documents collected from across the U.S. military in Afghanistan cover the war from 2004 to 2010, WikiLeaks said in a summary.
* Although founder Julian Assange has given few interviews recently, a website, www.wikileaks.org, and a Twitter feed, www.twitter.com/wikileaks, occasionally release material.
* Assange is an Australian who spends much of his time in Sweden. Earlier this year, he was accused of molestation by two women there, a charge being investigated by the Swedish prosecutor's office. A complaint about attempted rape led to an arrest warrant, but that was quickly dropped. Assange has denied all charges.
* Sweden's media laws are among the world's most protective for journalists. In addition, Sweden's Pirate Party, which advocates reform of copyright law, has agreed to host WikiLeaks' servers, giving it additional legal protection.
* WikiLeaks has no connection to the popular online encyclopedia Wikipedia.
(Writing by Eric Walsh and Doina Chiacu; editing by Mohammad Zargham)