WikiLeaks founder Julian Assange woke up in a British jail on Friday at the start of a likely lengthy extradition battle after a dramatic end to his seven-year stay in Ecuador's London embassy.

The U.N. human rights office urged judicial authorities to ensure that Assange, currently in British custody and the subject of an extradition request from the U.S., gets a fair trial. "We expect all the relevant authorities to ensure Mr. Assange's right to a fair trial is upheld by authorities, including in any extradition proceedings that may take place," U.N. human rights spokeswoman Ravina Shamdasani told a Geneva news briefing.

Edward Snowden, the former security contractor who leaked classified information about U.S. surveillance programs, said in a tweet that the arrest of Assange should be considered a violation of human rights after repeated statements issued by the U.N. calling for him to walk free.

Assange will now be at the heart of a legal and diplomatic tug-of-war, pitting him and his legions of supporters, including Russian authorities, against the U.S. justice system. His links to Russia continued through the years holed up in the Ecuadoran Embassy. Assange had long suspected that he was secretly wanted by Washington for his decision to publish a trove of classified Pentagon documents detailing alleged U.S. war crimes in Afghanistan and Iraq.