The head of Russia's GRU military intelligence agency that the West has blamed for a string of brazen attacks died on Wednesday after "a serious and long illness," the Russian Defense Ministry said.

State news agency TASS cited the ministry as saying Igor Korobov, 62, who ran the spy agency since 2016, had been made a Hero of Russia for his service in the post, the highest state award.

Britain has accused the GRU of attempting to poison former Russian spy Sergei Skripal and his daughter with a nerve agent in the city of Salisbury, the Netherlands has accused it of trying to hack the global chemical weapons watchdog, and U.S. intelligence agencies say it tried to hack the 2016 presidential election.

Russia denies all those allegations.

Speculation about Korobov's fate had been growing since an unconfirmed Russian media report that he had been summoned by President Vladimir Putin after the Skripal affair and severely criticised for the operation which left the Skripals alive and the GRU a target of mockery in the Western media.