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Assange faces allegations of sexual assault and rape in Sweden, which he denies. He says he fears Sweden could in turn extradite him to the United States to be tried for one of the largest leaks of classified information in U.S. history.
Thomas Olsson, one of Assange's lawyers, said the arrest warrant should be repealed because it cannot be enforced while Assange is in the embassy and the Swedish prosecutor had not considered the possibility of interrogating him in London.
"In light of the significant impact this has on Assange's ability to move freely and to live a normal life, we think that it is unreasonable to uphold the decision," Olsson told Reuters.
"As I see it, the arguments for the unreasonableness of the situation are very strong, so we have very strong hopes that the court will change the decision."
Ecuador, which has granted Assange political asylum, wants London to assure him safe passage to Quito. But Britain has surrounded the Ecuadorean embassy with police officers round the clock ready to detain him if he leaves it.
The South American country said last week that talks with Britain over Assange were at an impasse.