The US, France, Germany and Canada have agreed with the UK that the Russian government “almost certainly” approved the Novichok poisoning in Salisbury.
They have urged Russia to provide full disclosure of its Novichok programme.
The joint statement comes as the United Nations Security Council meets to discuss the attack on former Russian spy Sergei Skripal and his daughter Yulia in March and its fallout.
Russia has continued to deny any involvement.
The UK has named two men believed to be from Russia’s military intelligence service, the GRU, as the main suspects.
Theresa May told the Commons on Wednesday that the suspects had entered the UK on Russian passports using the names Alexander Petrov and Ruslan Boshirov.
She said the poisoning was “not a rogue operation” and was “almost certainly” approved at a senior level of the Russian state.
The statement from Mrs May, Emmanuel Macron, Angela Merkel, Justin Trudeau and Donald Trump said: “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.”
The leaders welcomed the progress in the investigation, but urged those with more information to go to UK authorities.
Meanwhile, the United Nations Security Council is meeting after British Prime Minister Theresa May named the two men allegedly responsible for the Skripal poisoning as Russian spies.