The threat from Russia is “real and active” but will be countered by Britain and its allies, the head of GCHQ has said.
Jeremy Fleming, director of the government's cyber intelligence agency, said an international partnership of allies was ready to reject the Kremlin's “brazen” determination to undermine international law.
His comments came after France, Germany, Canada and the US supported Prime Minister Theresa May's assertion that Russia was behind the Salisbury Novichok attack.
Speaking at the Billington Cyber Security Summit in Washington, Fleming said: “It's worth remembering that this was the first we had seen a nerve agent used in Europe since World War Two.
“That's sobering, and demonstrates how reckless the Russian state is prepared to be.”
He added: “The threat from Russia is real. It's active.
“And it will be countered by a strong international partnership of allies. Able to deploy the full range of tools from across our national security apparatus.”
Earlier this week May told MPs the attempted murder of former spy Sergei Skripal and his daughter Yulia in March was carried out by Russian military officers and “almost certainly approved at a senior level of the Russian state".
She said the two suspects charged by police, Russian nationals Alexander Petrov and Ruslan Boshirov, were officers from the Russian military intelligence unit known as the GRU.
The UK has obtained a European Arrest Warrant in case the men are found in the EU.
At a meeting of the UN Security Council earlier this week, Russia dismissed the UK's claims as “lies”, while the Kremlin called the accusations “unacceptable”.