Assange, aged 49, who spent almost seven years holed up in the Ecuadorian embassy in London, faces an 18-count indictment from the U.S. authorities accusing him of recruiting hackers to steal military secrets.

Assange, who sat behind a glass security screen at the back of the court, was formally rearrested on a new U.S. indictment which updated and broadened previous charges, brought mostly under the U.S. Espionage Act.

Assange told district judge Vanessa Baraitser he did not consent to be extradited, paving the way for a lengthy legal battle in London's most famous courthouse.

The indictment says Assange and WikiLeaks repeatedly sought, obtained, and disseminated information that the U.S. classified due to the serious risk that unauthorised disclosure could harm the national security.

A 200-page submission by Assange's barrister Edward Fitzgerald asserted that the prosecution was being pursued for ulterior political motives and not in good faith.

Fitzgerald said in the submission: "The request seeks extradition for what is a classic 'political offence'. Extradition for a political offence is expressly prohibited by article 4(1) of the Anglo-U.S. extradition treaty. Therefore, it constitutes an abuse of this court's process to require this court to extradite on the basis of the Anglo-U.S. treaty in breach of the treaty's express provisions."

Assange faces a prison term of up to 175 years in the U.S. if he is found guilty over the publication of secret intelligence and military documents.

A number of Assange supporters, including his partner Stella Morris, gathered outside the courthouse before the case opened Monday. The hearing in London is set to continue for a number of weeks.