MOSCOW (AP) – A military court on Wednesday gave a 13-year prison sentence to a retired Russian colonel who reportedly helped British intelligence unmask dozens of Russian agents.

Sergei Skripal was found guilty of passing along state secrets to Britain, said Anton Yeliseyev, an official at the Moscow District Military Court.

The 55-year-old Skripal was ordered to spend his prison term in a high-security penal camp.

His case was this year’s second espionage case in Russia involving Britain.

A white-haired Skripal was shown in televised footage standing in the cage typically used in Russian courtrooms, looking serious as the judge read the verdict.

Russia’s chief military prosecutor, Sergei Fridinsky, said Skripal received a lighter sentence than the 15 years demanded by prosecutors because he admitted his guilt and cooperated with the investigation.

The newspaper Izvestia reported Wednesday that Skripal was charged with spying for Britain’s MI6 foreign intelligence agency.

Skripal was accused of working over a period of several years for MI6 and of revealing the names of several dozen Russian agents working in Europe, Izvestia reported.

Officials said Skripal’s spying had seriously disrupted Russian espionage activities.

“His activities caused a significant blow to Russia’s external security,” court spokesman Yevgeny Komissarov was quoted as saying by the RIA-Novosti news agency.

State-run television in Russia quoted intelligence sources who compared Skripal’s spying to that of Soviet double agent Oleg Penkovsky, who spied for Britain and the United States during the height of the Cold War. He was shot by a firing squad in 1963.

The Federal Security Service, the main successor agency to the KGB, said Skripal had been recruited by British intelligence in the 1990s when he was working in the Russian armed forces. The service gave no further details.

Izvestia reported that Russian investigators believe Skripal received around $100,000 from MI6, for which he started working during a lengthy foreign posting from the mid-1990s.

Earlier this year, the Federal Security Service accused four British diplomats of espionage and said one of them had provided money for nongovernment organizations – accusations dismissed by Kremlin critics as part of a campaign to discredit NGOs.

The charges included allegations that the diplomats received secret information from a radio transmitter hidden in a rock.

The FSB also said that a Russian citizen who allegedly had contacts with British agents had been detained and confessed to espionage. The diplomats were not expelled.

Prosecutions on espionage charges have increased in Russia since the 2000 election of President Vladimir Putin, a former KGB colonel and one-time head of the FSB.

In 2004, arms control researcher Igor Sutyagin was convicted of treason for allegedly selling information on nuclear submarines and missile-warning systems to a British company that investigators claimed was a CIA cover.

A physicist, Valentin Danilov, was also convicted that year of selling classified information on space technology to China.