Mr Assange was arrested in Britain in December 2010 on an extradition warrant from Sweden,where he is wanted for questioning over allegations of rape and sexual abuse made by two women.
After losing a protracted legal battle to avoid extradition,which went all the way to Britain's Supreme Court,Mr Assange jumped bail and sought refuge in the Ecuadorean embassy in London last June. He has been inside the building ever since.
Khan was executive producer of a documentary film about WikiLeaks titledWe Steal Secrets, which recently premiered at the Sundance Film Festival in the US.
Khan said the film,directed by the Oscar-winning documentary maker Alex Gibney,sought to present a balanced view of the WikiLeaks story but Mr Assange had denounced it before seeing it.
''When I told Assange I was part of theWe Steal Secretsteam,I suggested that he view it not in terms of being pro- or anti-him,but rather as a film that would be fair and would represent the truth,''she wrote.
WikiLeaks ... has been guilty of the same obfuscation and misinformation as those it sought to expose.
Jemima Khan
''He replied:'If it's a fair film,it will be pro-Julian Assange.'''
Khan's article praised WikiLeaks for exposing corruption,torture,war crimes and cover-ups but criticised it for a''with us or against us''mentality that was detrimental to its cause.
She wrote that she was among those who had found the timing of the sexual abuse allegations against Mr Assange suspicious,as they came at the height of the furore over the revelations on WikiLeaks,but had come to the conclusion that the allegations had to be dealt with through Swedish due process.
''The women in question have human rights,too,and need resolution. Assange's noble cause and his wish to avoid a US court does not trump their right to be heard in a Swedish court,''she wrote,referring to Mr Assange's fears that Sweden could be a first stop on the way to an espionage trial in the United States.
''I don't regret putting up bail money for Assange but I did it so that he would be released while awaiting trial,not so that he could avoid answering to the allegations,''Khan wrote.
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Khan has not disclosed how much money she put up and whether she has had to surrender it since Mr Assange skipped bail.
Reuters