Britain and its allies will deploy a "full range of tools" against Russia after London accused two Russian agents of carrying out the attempted murder of former Russian spy Sergei Skripal and his daughter, a British spy chief said on Thursday.

British prosecutors on Wednesday charged two Russian nationals with the attack on the Skripals in the English city of Salisbury using the nerve agent Novichok.

Later, Prime Minister Theresa May said the men were officers in Russia's military intelligence service, the GRU, acting on orders from senior Kremlin figures, accusations Moscow has rejected as unacceptable.

In a speech in Washington on Thursday, Jeremy Fleming, Director of the GCHQ eavesdropping intelligence agency, said his staff had helped the "painstaking and highly complex investigation" into identifying those responsible for the Salisbury poisonings and action would now be taken.

"We have ascertained exactly who was responsible and the methods they used," Fleming told the Billington Cyber Security Conference according to extracts released by his office.

"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, and ready to reject the Kremlin's brazen determination to undermine the international rules based order."

Fleming's comments came after Britain, France, Germany, Canada and the United States pledged in a joint statement to work to disrupt "the hostile activities of foreign intelligence networks".