WikiLeaks advised journalists not to report 140 different "false and defamatory" statements about its founder Julian Assange, who has been holed up in the Ecuadorean embassy in London since June 2012.
It was not immediately clear what prompted the advice to media organisations, but WikiLeaks singled out Britain's Guardian newspaper for publishing what it said was a false report about Assange. The Guardian did not immediately respond late on Sunday to a Reuters request for comment.
The Australian set up WikiLeaks as a channel for publishing confidential information from anonymous sources. He is a hero to some for exposing what supporters cast as government abuse of power and for championing free speech, but to others he is a rebel who has undermined the security of the United States.
WikiLeaks angered Washington by publishing hundreds of thousands of secret U.S. diplomatic cables that laid bare often highly critical US appraisals of world leaders from Russian President Vladimir Putin to members of the Saudi royal family.
"There is a pervasive climate of inaccurate claims about WikiLeaks and Julian Assange, including purposeful fabrications planted in large and otherwise 'reputable' media outlets," Wikileaks said an email sent to media organisations and marked "Confidential legal communication. Not for publication."