Assange, who is holed up in Ecuador's embassy in London, refused to cooperate with Oscar-winning director Alex Gibney's "We Steal Secrets: The Story of WikiLeaks".
"WikiLeaks has never co-operated with Universal or Alex Gibney," Assange said in an email to The Sydney Morning Herald today.
"This US filmmaker has lost objectivity and perspective, probably as a result of WikiLeaks' decision to not engage with them."
WikiLeaks said on its website that Gibney's film about the organisation, due to screen at the Sydney Film Festival this month, contains errors of fact, selective editing and misrepresentations.
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"There are no factual errors and there is nothing misleading in the film," the paper quoted him as saying. "It is a series of Julian's opinions."
The Herald also quoted the director as likening Assange to the Wizard of Oz -- "that moment where Toto pulls the curtain away and you see a man desperately manoeuvering the levers trying to burnish his image".
Gibney's film is set to focus on Assange and US Army whistleblower Bradley Manning, who is accused of slipping 250,000 diplomatic cables and 500,000 classified military documents to WikiLeaks.
The US Army private faces a court-martial starting today. Washington is still investigating whether Assange encouraged Manning to disclose more details, in which case the Australian may be prosecuted in the United States.
Assange is fighting extradition from Britain to Sweden, where authorities want to question him over alleged sex crimes.
He has been living inside Ecuador's embassy since June 2012 as Britain refuses him safe passage to the left-leaning Latin American nation.
Gibney's film also reportedly includes the claim that the Australian former hacker sought payment for an interview and claimed the market rate was USD 1 million.