Russia announced today it would seek a 20-year prison term for a top spy whose cooperation with the United States led to last year's embarrassing expulsion of 10 Russian sleeper agents.

The Federal Security Service (FSB) said it has concluded its probe into the former deputy head of its US clandestine operations department and charged him with treason and desertion.

The suspect, named as Alexander Poteyev, is believed to be residing in the United States and will be tried in absentia.

"The FSB investigative department has concluded its investigation into Russian citizen A. N. Poteyev," news agencies quoted an FSB statement as saying.

"The indictment was submitted to the Moscow district military tribunal for a hearing on April 21," the Russian security service statement added.

The exposure of the spies -- who included the media sensation Anna Chapman and others who worked on the US East Coast -- left some intelligence officials conceding that their US surveillance programme had been dealt a brutal blow.

Former spy and current Prime Minister Vladimir Putin used a national television appearance in December to call the double agent a "pig" who will "regret it a thousands times over".

News reports said Poteyev was the deputy head of the US department of Directorate C -- an agency involved in placing long-term agents in foreign countries who try to pass of as locals.

"He fled Russia a few days before Russian President Dmitry Medvedev's June trip to Washington and is currently in the United States," Interfax quoted an unnamed security official as saying.

The United States announced the 10 Russians' arrest just days after Medvedev's visit and eventually exchanged them for four Russians who allegedly spied for the West.