Russian cyber intelligence officers tried to hack the UK’s Foreign Office, a British diplomat has said.
Peter Wilson, the UK ambassador in The Hague, said Russian intelligence officers tried to compromise Foreign Office systems with an attack in March.
The accusation comes after Dutch security services said they expelled four Russians over a cyber plot against the global chemical weapons watchdog.
Moscow said the allegations were “not backed by any proof”.
In a statement with Dutch Prime Minister Mark Rutte, Theresa May said “joint operations” had shone “further light on the unacceptable cyber activities of the Russian military intelligence service, the GRU”.
Mrs May said the attempted hack of the Organisation for the Prohibition of Chemical Weapons (OPCW) demonstrated the GRU’s “disregard for the global values”.
The watchdog, based in the Hague, was examining the 4 March Salisbury attack.
Mr Wilson said targeting of the OPCW headquarters in May followed unsuccessful attacks by the GRU on the Foreign Office in March and on the defence laboratories at Porton Down, which was also investigating the Salisbury poisoning, in April.