Julian Assange has hit back at Hillary Clinton after she labelled the WikiLeaks founder a "nihilistic opportunist" on Australian television.

The Australian 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 Mrs Clinton's presidential campaign last year.

Mrs Clinton told ABC TV's Four Corners program on Monday 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 Mr Trump.

Mr Assange has consistently denied the Russian government was the source.

"I think Assange has become a nihilistic opportunist who does the bidding of a dictator," Mrs Clinton said.

"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?"

AAP

Prior to the broadcast on Monday night, Mr Assange took aim at Mrs Clinton on Twitter, saying: "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."

In a separate tweet, he said: "On Clinton's 'timing' conspiracy theory. That we had a pending publication about to launch on the election was everywhere in the media for days. We were meant to launch that morning. It is the Trump tape that was moved forward from Monday to Friday."

Mr Assange also took aim at the ABC, saying the broadcaster had not offered him a right of reply to Mrs Clinton's charges, despite the executive producer of the program suggesting otherwise.

We have no record of such a request but regardless its pre-dates your Hillary Clinton interview by weeks and cannot be a right of reply to it. It is deceptive to suggest otherwise. — Julian Assange 🔹 (@JulianAssange) October 16, 2017

"(at) 4corners (at) ABC I note that (at) ABC failed to obtain my response in what seems to be a clear violation of its Code of Practice before promoting Hillary Clinton's defamatory statements. No surprise. The PM doesn't even have the courage to congratulate our Nobel Peace Prize winners."

Four Corners' executive producer Sally Neighbour offered Mr Assange a chance to respond via Twitter but he seemed to reject the offer.

"You think the reward for breaking your code of conduct, by letting a notorious liar defame an Australian political refugee without gaining his response prior to its promotion & broadcast (although you had time to do so) is an interview you wouldn't otherwise get after the event?" Mr Assange tweeted.

He later tweeted: "No wonder Australian state TV (at) ABC (at) 4corners broke their code of conduct over their Hillary Clinton interview. Look at the extreme unprofessionality of the ABC 'executive producer' behind it".

No wonder Australian state TV @ABCTV @4corners broke their code of conduct for Hillary Clinton. Look at the extreme unprofessionality of the tax payer funded 'executive producer' behind it. Pathetic. https://t.co/1M4nbmt4hy pic.twitter.com/b5yuBx4aTZ — Julian Assange 🔹 (@JulianAssange) October 16, 2017

The accompanying screenshot appeared to show Ms Neighbour had re-tweeted: "Assange is Putins b****. We all know it! (hashtag)4Corners"

Ms Neighbour later tweeted: "Mea culpa (at) JulianAssange, that RT [retweet] was a mistake, since undone.We are offering you full right of reply on (hashtag)4Corners.Name a date,we'll be there".

Mr Assange has spent five years inside the Ecuadorian embassy in London.

He remains in the embassy over fears he will be extradited to the US.