The Russian special services are accusing Paul Whelan of spying for their U.S. colleagues, his lawyer said.

"The investigators believe he was spying for the U.S. special services," lawyer Vladimir Zherebenkov told Interfax.

The case against Whelan is being investigated by the Russian Federal Security Service. He is charged with espionage.

In the coming hours the Moscow City Court will hear the defense lawyers' appeal against the decision to prolong Whelan's arrest by a further three months.

The hearing is attended by U.S. embassy official Richard Hanrahan, who is in charge of the observance the rights of U.S. citizens in Russia.

Officials from the Irish, Canadian, and British embassies, who attended earlier hearings of the Whelan case, have ignored this hearing.