It was not immediately clear what prompted the advice to media organisations,but WikiLeaks singled out Britain'sGuardian newspaper for publishing what it said was a false report about Assange. TheGuardian 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 US 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 Not for publication."
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"Consequently journalists and publishers have a clear responsibility to carefully fact-check from primary sources and to consult the following list to ensure they are not spreading,and have not spread,defamatory falsehoods about WikiLeaks or Julian Assange."
WikiLeaks did not respond to repeated requests for comment.
The 5000-word email included 140 statements that WikiLeaks said were false and defamatory,such as the assertion that Assange had ever been an"agent or officer of any intelligence service".