A retired colonel from Russia's counterintelligence agency was convicted Wednesday of spying for the United States and sentenced to 18 years in prison — the latest in a string of spy cases amid tensions in Russia-U.S. relations.

District Military Court spokeswoman Irina Zhirnova said the Moscow court had convicted Valery Mikhailov of passing state secrets to the U.S. Central Intelligence Agency. She said Mikhailov would be stripped of his rank and sent to a high-security prison.

She said Mikhailov, a retired Russia's Federal Security Service, or FSB, colonel had contacted CIA representatives in Moscow and handed them confidential information. Zhirnova wouldn't say when Mikhailov passed the data, or give any further details about Mikhailov or detail the charges against him.

Mikhailov's case is the latest in a raft of espionage convictions in Russia this year.

Last week, a retired Russian military officer was also found guilty of spying for the U.S. and handed a 12-year prison sentence. That followed the conviction earlier last month of a defense company worker who received an eight-year sentence on charges of betraying missile secrets.

And in February, a military officer who oversaw missile tests at the Plesetsk Launchpad in northern Russia was convicted on charges of providing the CIA with secret information on new missiles and sentenced to 13 years in prison.

The spy trials come as U.S.-Russian relations have soured over U.S.-led NATO missile defense plans for Europe, which Moscow sees as a potential threat to its nuclear forces, the Syrian crisis and other disputes.

Vladimir Putin, re-elected to third term as president in March, had given his campaign a distinctly anti-American flavor, accusing Washington of staging the mass protests against his 12-year rule in an attempt to weaken Russia.

He has snubbed the Group of Eight Summit in Chicago last month in a move widely seen widely as an expression of his irritation with Washington.