Hillary Clinton has attacked Julian Assange for allegedly damaging her chances of becoming US president, slamming the Australian as a “nihilistic opportunist” in an explosive interview.

Mrs Clinton’s claims – set to feature on ABC TV’s Four Corners on Monday evening – surround the 2016 US election and WikiLeaks founder Mr Assange, whom she dubbed “a tool of Russian intelligence”.

Mr Assange and WikiLeaks are the subject of a US Justice Department investigation following the publishing of thousands of documents, including emails, that arguably derailed Mrs Clinton’s bid to become US president.

“Assange has become a kind of nihilistic opportunist who does the bidding of a dictator [Vladimir Putin],” she alleged.

“WikiLeaks is unfortunately now practically a fully owned subsidiary of Russian intelligence.

“He’s [Assange] a tool of Russian intelligence. If he’s such a martyr of free speech, why doesn’t WikiLeaks ever publish anything out of Russia?”

Mr Assange responded to the claims on Twitter, posting: “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.”

Mr Assange has been inside the Ecuador embassy in London since 2012. Photo: AAP

He also accused the ABC of failing “to obtain my response … before promoting Hillary Clinton’s defamatory statements”.

In the Four Corners interview, Mrs Clinton added that she was convinced Russian President Vladimir Putin was behind a campaign against her.

“I think that their intention coming from the very top with [Mr] Putin was to hurt me and to help [US President] Donald Trump,” she said.

“Our intelligence community and other observers of Russia and [Mr] Putin have said he held a grudge against me because as secretary of state, I stood up against some of his actions, his authoritarianism.

“But it’s much bigger than that. He wants to destabilise democracy, he wants to undermine America, he wants to go after the Atlantic alliance and we consider Australia an extension of that.”

WikiLeaks published hacked emails relating to Mrs Clinton’s campaign over four months in 2016 as the US election approached.

And the 69-year-old said the timing of those leaks was shown clearly when, in October last year, a recording of Donald Trump making comments about sexually harassing women was released.

Less than one hour later, more than 2000 emails from Mrs Clinton’s presidential campaign chair, John Podesta, were published by WikiLeaks.

“I’ve no doubt in my mind that there was some communication if not coordination to drop those the first time in response to the Hollywood Access tape,” she said.

The full interview with Mrs Clinton will air on ABC’s Four Corners on 8.30pm (AEDT) on Monday.