But Russian Foreign Ministry spokeswoman Maria Zakharova dismissed the new accusations, calling them "big fantasies".
In an interview broadcast on the Kremlin-backed RT network, the two men admitted visiting Salisbury but denied carrying out the Novichok poisoning, saying that the objective of their brief trip was to visit the city's historic landmarks.
Among other things the ministers agreed to share cyber capabilities while NATO Secretary General Jens Stoltenberg used the occasion to condemn Russian Federation for its alleged hacking operations.
"We are going to actually make it clear that where Russian Federation acts, we are going to be exposing that action", Williamson said.
U.S. Defense Secretary Jim Mattis said he agreed with the British and Dutch assessments.
He said the agents had planned to target an OPCW in laboratory in Switzerland too.
The Dutch authorities named four GRU operatives who travelled to Amsterdam and attempted to hack into the Organisation for the Prohibition of Chemical Weapons network directly. The worldwide organization was investigating the use of chemical weapons in Syria and the poisoning of former GRU officer Sergei Skripal and his daughter, Yulia, in Salisbury in March.
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And now, the United Kingdom and the Dutch governments have revealed a huge amount of new intelligence about how the GRU has been operating across the world, namely its attempts to hack the OPCW chemical weapons inspectors' headquarters in the Hague, the computers of the Foreign Office in London and the work of the Porton Down military laboratories in Wiltshire.
Officials believe the scale of that joint action against Russian Federation took the Kremlin by surprise and put them on the back foot.
The four men flew from Moscow to Amsterdam on April 10 on official passports, where they were met by a Russian embassy official. Reuters was not immediately able to contact them.
But a federal indictment announced on Thursday charges that Russian spies waged a long-running campaign to undermine investigations into doping activities by Russian athletes during the 2014 Winter Olympics in Sochi.
In a news conference in The Hague, Dutch Defence Minister Ank Bijleveld called on Russian Federation to cease its cyber activities that aim at "undermining" Western democracies.
Russia's military spy service has been behind a wave of massive cyber attacks in the recent years, with targets ranging from the worldwide chemical weapons watchdog group to the probe into the downing of a Malaysian Airlines plane over Ukraine, officials said Thursday.
They spoke after officials from both countries blamed the GRU for a series of attacks against the worldwide chemical weapons watchdog and other agencies, including the World Anti-Doping Agency and groups investigating the 2014 Malaysian Airlines crash over Ukraine.
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"The GRUs actions are reckless and indiscriminate: they try to undermine and interfere in elections in other countries", said British Foreign Secretary Jeremy Hunt.
"Our message is clear: together with our allies, we will expose and respond to the GRU's attempts to undermine global stability", he said.
Britain blames the secretive military intelligence unit for the nerve agent attack in March on former Russian spy Skripal and his daughter, Yulia, in the English city of Salisbury.
Foreign Secretary Jeremy Hunt said Russian Federation could now face further sanctions following the "hard evidence" presented on Thursday, dismissing Moscow's assertions of innocence as "fake news".
Hunt said the hacking attempt at the OPCW was further proof of Moscow's role in the poisoning.
In some of the strongest language used by the West since the Cold War, Britain has said Russian Federation was acting like a "pariah state".
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