Russia appointed Major General Igor Sergun as the new chief of the GRU military intelligence service, the country's biggest espionage agency, news agencies quoted a Defense Ministry spokesman as saying on Monday.
No other details were given about the new head of the GRU, an organization so secretive it has neither a spokesman nor a web site.
The state-run newspaper Rossiiskaya Gazeta described Sergun as a career spy and cited sources as saying he had served as deputy to the outgoing GRU chief Alexander Shlyakhturov.
Defense Ministry spokesman Igor Konashenkov told Interfax that Shlyakhturov, 64, was removed after reaching retirement age for military servicemen.
The Kommersant newspaper, citing unidentified sources on Saturday, said Shlyakhturov, who was appointed by President Dmitry Medvedev in April 2009, had left his post to head the board of OAO Korporatsiya MIT, which develops nuclear missiles.
The Russian military intelligence service, known by its Russian acronym GRU, has agents spread across the globe.
Created in 1918 under revolutionary leader Leon Trotsky, it answers to the chief of the general staff, one of the three people who control Russia's portable nuclear briefcase. Shlyakhturov's predecessor, General Valentin Korabelnikov, was seen to have been dismissed for opposing Kremlin-backed military reforms. But Shlyakhturov is viewed as an ally of Defense Minister Anatoly Serdyukov, who has cut the number of servicemen and reorganized the armed forces command.
Unlike the Soviet-era KGB secret police, the GRU was not split up when the Soviet Union collapsed, although the organization has lost turf wars with the KGB's main successor, the FSB, over recent years, according to local media.
Russia's most powerful man, Vladimir Putin, served as a KGB spy in East Germany in the 1980s and later became director of the FSB. In 2006, he visited the new Moscow headquarters of GRU, where he was shown shooting a pistol on a firing range.