Former attorneys-general have urged the release of Julian Assange, calling on the Prime Minister to intensify efforts to free him.

In a joint letter to Prime Minister Anthony Albanese, nine former attorneys-general, including those at a federal, state and territory level, labelled Mr Assange’s treatment in prison “deeply troubling”, pushing the government to do more for his release.

Assange, an Australian citizen, published a trove of classified documents more than a decade ago.

He has been in prison in the UK for more than four years and is fighting extradition to the US to face espionage charges.

Signatories of the joint letter include former federal attorney-general Michael Duffy, former ACT attorney-general Bernard Collaery, former Victorian attorney-general Rob Hulls and former NSW attorney-general Bob Debus.

“We believe that the treatment of Julian Assange, as opposed to Australian journalists, is deeply troubling given that in both cases the right of the public to know about war crimes, whenever and wherever they are committed, is crucial,” they said in the letter.

“In relation to the ongoing incarceration of Mr Assange, we say enough is enough and we look to you and your government to do all you can to satisfactorily resolve this matter quickly.”

Since winning office in 2022, the Albanese government has been advocating for the US pursuit of Assange to end.

Mr Albanese will meet US President Joe Biden at the White House in October.

The letter said the US charging Mr Assange under its own espionage laws was a concerning development.

“We believe that this sets a very dangerous precedent and has the potential to put at risk anyone, anywhere in the world, who publishes information that the US unilaterally deems to be classified for security reasons,” the letter said.

“This action should be of real concern to the government because of its impact on journalists and whistleblowers.”

The statement from the attorneys-general comes after US ambassador Caroline Kennedy flagged the possibility of a plea deal in Assange’s case.

In an interview with the Sydney Morning Herald, Ms Kennedy said there “absolutely” could be a resolution, and flagged the possibility of a plea deal between the US and Australia.

The comments raised hope among Assange supporters that the US case against him could be dropped.

-AAP