US vice president Joe Biden blasted Julian Assange as a dangerous “hi-tech terrorist” and said Washington was exploring a legal pursuit of the WikiLeaks founder.

Mr Biden made the comments as Mr Assange spent his third full day under “mansion arrest” at a friend’s house in eastern England while he fights extradition to Sweden, where he is wanted for questioning over allegations of sex crimes.

The Australian has enraged the US by obtaining a cache of some 250,000 US diplomatic cables and slowly releasing the documents through his whistleblowing website, often causing huge embarrassment in Washington.

Mr Assange voiced fears last week that the US would try to extradite him on charges related to the leaked cables, and Biden said the US Justice Department was examining how to take legal action against Assange. When asked whether he thought Mr Assange was a hi-tech terrorist or a whistleblower akin to those who released the Pentagon Papers – a series of top-secret documents revealing US military policy in Vietnam – Biden said: “I would argue that it’s closer to being hi-tech terrorist.”

Media reports suggest that US prosecutors are trying to build a case against him on the grounds that he encouraged a US soldier, Bradley Manning, to steal US cables from a government computer and pass them to WikiLeaks.

Mr Assange has denied knowing Mr Manning.

A report by congressional researchers said the Espionage Act and other US laws could be used to prosecute Mr Assange, but there is no known precedent for prosecuting publishers in such a case.

Mr Assange is staying at Ellingham Hall, the mansion in eastern England of journalist friend Vaughan Smith, as part of the conditions of bail, which he was granted by London’s High Court on Thursday.

He must also report daily to a nearby police station and wear an electronic tag.