Russian spies targeted Britain's Foreign Office, computers at Porton Down and the chemical weapons watchdog, officials have said.
He said: 'If anyone had any questions in their mind about Russian military involvement in the Salisbury attacks, this will put to rest those doubts because we have evidence of the Russian military launching a cyber-attack on the very global organisation in the Netherlands set up to investigate those novichok attacks.
Al Jazeera's Paul Brennan, speaking from London, said Thursday's reaction is notable.
In a statement, it said: "As is traditional, it is not backed by any proof and is another element in an anti-Russian campaign being conducted by the British government".
"Western spy mania is gathering pace", a Russian foreign ministry representative told AFP.
The Netherlands released copies of passports of the four men, which identified them as Alexey Minin, Oleg Sotnikov, Evgenii Serebriakov and Aleksei Morenets, all in their 30s or 40s.
This version removes the incorrect reference to the Organization for the Prohibition of Chemical Weapons as a United Nations organization.
The Russians set up a auto full of electronic equipment in the vehicle park of a hotel next to the Organisation for the Prohibition for Chemical Weapons in The Hague in a bid to hack its computer system, it said.
Sergei Skripal and his daughter Yulia recovered from poisoning after lengthy stays in hospital. Between 2016 and 2018 they also exchanged emails and private messages with some 186 reporters "in an apparent attempt to amplify the exposure and effect of their message", the Justice Department said in a news release.
"We intercepted it and expelled the four men from the country".
Russian President Vladimir Putin, himself a former KGB spy, said on October 3 that Mr. Skripal, a GRU officer who betrayed dozens of agents to Britain's MI6 foreign spy service, was a "scumbag" who had betrayed Russia.
He said the agents had planned to target an OPCW in laboratory in Switzerland too.
At a news conference in The Hague, Bijleveld called on Russian Federation to cease its cyber activities aimed at "undermining" Western democracies.
A British Whitehall official said that the 4 men were "caught in flagrante", and added the "technicolour" detail of the items found would be embarrassing to the Russians: "For a GRU operative to get caught with all that equipment would be seen by them as a pretty bad day". Around that time the OPCW was working to independently verify the United Kingdom's analysis of the chemical weapons used in the poisoning of the Skripals in Salisbury'.
"We are going to actually make it clear that where Russian Federation acts, we are going to be exposing that action", Williamson said.
NATO Secretary General Jens Stoltenberg has warned Russian Federation to halt its "reckless" behavior amid a series of global cyberattacks blamed on Moscow, and says NATO allies stand united behind the U.K. and Dutch governments.
Moscow's feared GRU cyber unit nicknamed "Sandworm" tried and failed to infiltrate UK IT systems as part of a series of attacks across Europe this year.
"We remain very alert about this", she said.
The revelations of the Hague operation do not just illustrate global cooperation, but also reveals the extent of western intelligence capabilities.
Seven Russian intelligence officers were indicted for hacking the computers of anti-doping sports agencies and other organizations around the world, the Justice Department said Thursday.
The same level of confidence is attached to a "hack against email accounts belonging to a small (unnamed) UK-based TV station".
Ties between Britain and Russian Federation are at rock bottom after a nerve agent attack targeting former Kremlin agent Sergei Skripal in the English city of Salisbury.