Assange has been at Ecuador's London embassy since last week. An officer with the Metropolitan Police gave him a note Thursday advising him to report to a police station "at a time of our choosing," police said.
"Our advice is that asylum law both internationally and domestically takes precedence over extradition law so almost certainly not," Assange said in an interview with the BBC.
Sweden is seeking Assange's extradition for an investigation into a sexual assault charge. He says he fears that is cover for plans to extradite him to the United States, where he could face charges connected to WikiLeaks' publication of U.S. diplomatic cables.
Ecuador has made no decision on asylum. Assange, who had been under house arrest in Britain, described the Embassy staff as "warm and generous" and said they had taken care of his "basic needs."
"This is standard procedure in extradition cases and is the first step in the removal process," police said in a statement about the order. "He remains in breach of his bail conditions and failure to surrender would be a further breach of those conditions and he is liable to arrest."