Kevin Rudd says Julian Assange would pay an "unacceptable" and "disproportionate" price if he is extradited to the United States, arguing the WikiLeaks founder should not take the fall for Washington's failures to secure its own classified documents.

In a significant intervention into Mr Assange's extradition fight, the former Australian prime minister said US prosecutors had not made any specific allegations that anyone was seriously harmed as a consequence of the release of highly classified documents relating to the Iraq and Afghanistan wars in 2010.

Former prime minister Kevin Rudd says Julian Assange does not deserve to face an effective life sentence in the United States. Credit:Alex Ellinghausen

The Morrison government is resisting a rising tide of demands to intervene in the case of the 48-year-old Australian citizen, as his supporters grow increasingly concerned over his deteriorating health in a British prison.

Mr Rudd, himself targeted in WikiLeaks' publication of more than 250,000 leaked diplomatic cables nine years ago, said while he had "serious reservations" about Mr Assange's character and conduct, he did not believe he should be extradited to face an "effective life sentence" in the US.