Russia’s top human rights official said Thursday that it was impossible to extradite whistleblower Edward Snowden to the United States.

“According to international conventions, a person who has requested temporary asylum must not be handed over,” the head of the presidential human rights council, Mikhail Fedotov, told the Interfax news agency.

Mr Fedotov also argued that, because Mr Snowden was still in the transit zone of Sheremetyevo airport, Moscow cannot hand him over because he is legally not in Russia. “Whatever happens, we can do nothing to please our American partners,” he said.

The whistle-blower has been stuck at the airport for four weeks. Washington insists that Mr Snowden should be handed over to the US, where he is sought on espionage charges.

The State Department said Wednesday that the US would be “deeply disappointed” if Moscow allowed him to leave the transit zone.

Earlier Wednesday, US Secretary of State John Kerry spoke by telephone with Russian Foreign Minister Sergei Lavrov.

Mr Snowden had been widely expected to emerge from the transit zone Wednesday. However, his Russian lawyer said after meeting him at the airport that unspecified bureaucratic difficulties had held him up.

The US ambassador to Russia, Michael McFaul, said Thursday that the US is not asking for “extradition,” but simply for “the return” of Mr Snowden. “We have sent many people back to Russia,” he wrote on Twitter.

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