General Igor Korobov, the head of Russia’s GRU military intelligence agency, has reportedly died at the age of 62 after what Moscow said was “a serious and long illness”.

Korobov and the GRU were both linked to the nerve agent attack in the UK on ex-Russian spy Sergei Skripal and his daughter Yulia in the British city of Salisbury in February.

Since taking over the highly secretive GRU, which retained its Soviet-era functions after the Soviet Union collapsed and the KGB was dissolved in December 1991, Korobov oversaw a string of brazen attacks on Western institutions that included hacking into the Netherlands’ chemical weapons watchdog and breaking into the Democratic Party’s server during the 2016 US presidential elections.

Korobov had come under intense scrutiny, however, from Russia’s intelligence community after the failure of the Skripal attack. The ease by which British intelligence and the investigative reporting website Bellingcat positively identified the two GRU field operatives who were responsible for the attack may have contributed to Korobov, a recipient of the Hero of Russia, the nation’s highest honour, having fallen out with Vladimir Putin.

Speculation had been growing about Korobov’s fate after unconfirmed opposition reports from inside Russia said he had been personally summoned to the Kremlin for an audience with Putin to explain why his agents had failed in their attempt to eliminate Skripal.

According to the reports, Putin – himself a former KGB colonel and ex-head of its successor, the FSB – was incensed at the handling of the Skripal affair and help Korobov responsible for allowing the GRU to be the target of widespread mockery in the Western media and intelligence community.

Prior to the announcement of his death, there had been no indication that Korobov was suffering from poor health, but his noticeable absence from a Putin-led ceremony earlier this month that marked the centenary of the GRU added further speculation as to his immediate fate.

With Korobov no longer at the helm, Putin is most likely to appoint a successor that will be closer to the traditions of the GRU, which has typically worked in the shadows. with few public appearances by any of its agents or those who are in charge. Korobov was frequently seen in public and had been included on the US and EU’s sanctions lists for having seen covert operations both in Europe and the United States.