Hillary Clinton has slammed WikiLeaks' Australian founder Julian Assange, calling him a "nihilistic opportunist" and claiming he worked with Russia to damage her chance of becoming US president.
Mr Assange and WikiLeaks are under investigation by the US Justice Department over the publication of top secret documents and thousands of emails from Democratic National Committee officials that undermined Ms Clinton's presidential campaign last year.
In response to the claims, Mr Assange - who has spent five years bunkered down in London's Ecuadorian Embassy - tweeted that there was something wrong with Ms Clinton.
"There's something wrong with Hillary Clinton. It is not just her constant lying. It is not just that she throws off menacing glares and seethes thwarted entitlement. Watch closely. Something much darker rides along with it. A cold creepiness rarely seen," he wrote.
Ms Clinton said the material was stolen as part of a concerted operation between Russia, WikiLeaks and people in the US, who she said wanted to "weaponise that information" by denigrating her campaign against Republican billionaire Donald Trump.
"I think Assange has become a nihilistic opportunist who does the bidding of a dictator," Ms Clinton told ABC TV's Four Corners.
"He's a tool of Russian intelligence.
"If he's such a martyr of free speech, why doesn't WikiLeaks ever publish anything coming out of Russia?"
US intelligence officials have blamed Russia for stealing the Democrats' emails and documents as part of a deliberate effort to wreck Ms Clinton's chances of becoming president.
They claim that WikiLeaks acted with Russian intelligence in publishing the documents.
Mr Assange has denied that the Russian government was the source behind the leaked documents.
In this June 5, 2017 file photo, former Secretary of State Hillary Clinton speaks in Baltimore. Source: AAP
Ms Clinton said the decision to leak the documents was linked to Mr Putin's desire to destabilise democracy and undermine the US, as well as the relationship America has with it allies including Australia.
She also believed that Mr Assange's personal dislike of her was a factor.
"I had a lot of history with him because I was secretary of state when WikiLeaks published a lot of very sensitive information from our State Department and our Defence Department," Ms Clinton said.
Mr Assange has spent five years seeking refuge inside the Ecuador embassy in London to avoid extradition to Sweden to answer sexual assault charges.
While the charges were recently dropped, Mr Assange has remained in the embassy amid fears he could be extradited to the US to face charges for releasing classified information.
