The Australian is on bail in Britain fighting a bid by Sweden to extradite him over sex assault claims, but Washington is believed to be considering how to indict him over the leaking of thousands of US diplomatic cables.
Mr Assange told The Guardian it would be "politically impossible" for Britain to send him across the Atlantic, adding that the government of Prime Minister David Cameron would want to show it had not been "co-opted" by Washington.
"Legally the UK has the right to not extradite for political crimes. Espionage is the classic case of political crimes. It is at the discretion of the UK government as to whether to apply to that exception," he said.
He said US authorities were "trying to strike a plea deal" with Bradley Manning, the US army soldier suspected of providing WikiLeaks with the cables.
Mr Assange added that if the United States succeeded in getting him extradited from Britain or Sweden, then there was a "high chance" of him being killed "Jack Ruby-style" in an American prison.
Ruby, a nightclub owner, shot dead Lee Harvey Oswald at a police station in Dallas, Texas days after Oswald was arrested for the assassination of US President John F. Kennedy in 1963.
Ruby's alleged links to organised crime sparked conspiracy theories about his involvement in an overall plot surrounding the assassination of Kennedy.
Mr Assange has previously said that he and other WikiLeaks staff have received death threats since the website began to release a cache of around 250,000 secret US State Department cable in November.
The 39-year-old has been staying at a friend's country mansion in eastern England since his release from jail last week on strict bail conditions that include reporting to police daily and wearing an electronic tag.
A court in London is due to hold a full hearing on the Swedish extradition request starting February 7.
Julian Assange wishes to avoid deportation to Sweden so he won't have to face
a criminal trail in Sweden. His holiday at his friend's country mansion will end
on January 11, 2011 when he most probably will be and should be deported to
Sweden who will no doubt, deport him to Australia, if the United States does not
come up with charges that may well be entirely appropriate.