The leaders of Britain, the United States, France, Germany and Canada said Thursday they had "full confidence" that the Novichok attack suspects were officers from Russia's military intelligence service.
In a joint statement reiterating their "outrage", the five leaders also said they were completely confident the attempted killing of former Russian double agent Sergei Skripal on British soil in March "was almost certainly approved at a senior government level" in Russia.
They also urged Moscow to come clean to the organisation for the Prohibition of Chemical Weapons (OPCW) about its Novichok programme.
The leaders added they would strengthen their activities to defend their societies against "malign state activity" and disrupt the hostile actions of foreign intelligence networks.
"We, the leaders of France, Germany, the United States, Canada and the United Kingdom, reiterate our outrage at the use of a chemical nerve agent, known as Novichok, in Salisbury on March 4," they said in the statement, issued in London.
They welcomed the progress made in the investigation and the attempted murder charges brought against Russian suspects Alexander Petrov and Ruslan Boshirov, announced by Britain on Wednesday.
They also noted the OPCW's findings that "the exact same chemical nerve agent" was used in the fatal poisoning of Dawn Sturgess. She was the girlfriend of Charlie Rowley, who had picked up a fake perfume bottle containing Novichok.
"We urge Russia to provide full disclosure of its Novichok programme to the OPCW," they said.
"We have full confidence in the British assessment that the two suspects were officers from the Russian military intelligence service, also known as the GRU, and that this operation was almost certainly approved at a senior government level."
They said the mass expulsion of undeclared GRU officers in Russian embassies in the wake of the Salisbury attack had disrupted the service's activities.
"Yesterday's announcement further strengthens our intent to continue to disrupt together the hostile activities of foreign intelligence networks on our territories, uphold the prohibition of chemical weapons, protect our citizens and defend ourselves from all forms of malign state activity directed against us and our societies."
A Downing Street spokesman said Prime Minister Theresa May spoke to US President Donald Trump on Tuesday, Canadian leader Justin Trudeau Wednesday and French President Emmanuel Macron and German Chancellor Angela Merkel earlier Thursday.