Washington has sought the extradition of Assange over his role in one of the biggest ever leaks of classified information, accusing him of putting lives in danger by releasing vast troves of confidential U.S. military records and diplomatic cables.

He has now spent nine years in jail or self-incarceration in Britain, and both Assange's fiancée Stella Moris and the British judge overseeing the extradition request have warned he may not survive a process to send him across the Atlantic.

"If Biden really wants to break with the Trump legacy, then he has to drop the case," Moris told Reuters in an interview. "They can't maintain this prosecution against Julian while saying that they defend a global press freedom."