The Supreme Court is expected to rule within a few weeks, the Australian Broadcasting Corp. reported. If he loses, Assange has no further appeals available in Britain.
Swedish authorities are seeking to question Assange on allegations that he committed sexual assault.
Clare Montgomery, representing the Swedish Judicial Authority, told the court Thursday that arrest warrants can be issued by prosecutors, The Guardian said. Assange's lawyer argued Wednesday that warrants must be issued by judges or other neutral parties.
Montgomery said that fairness comes in guaranteeing a trial by an impartial court and that the decision to arrest someone is necessarily one-sided.
Assange, an Australian citizen, has lived in a number of countries since founding Wikileaks. He is under house arrest in Britain.
He is believed to be more concerned about extradition to the United States, where Bradley Manning, a U.S. soldier, faces court martial for leaking thousands of pages of classified material to Wikileaks.
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