The international chemical weapons watchdog has confirmed the UK's analysis of the type of nerve agent used in the Russian ex-spy poisoning, wrote BBC.
The Organisation for the Prohibition of Chemical Weapons did not name the nerve agent as Novichok, but said it agreed with the UK's findings on its identity.
Russia has denied it was behind the attack on Sergei and Yulia Skripal in Salisbury, as Theresa May has claimed.
Foreign Secretary Boris Johnson said: "There can be no doubt what was used."
He added: "There remains no alternative explanation about who was responsible - only Russia has the means, motive and record."
A team from the OPCW visited the UK on 19 March, 16 days after the Skripals were found slumped on a park bench in Salisbury and taken to hospital, along with a police officer who was among the first on the scene.
Ms Skripal was discharged from hospital on Monday but the 33-year-old has said her father is "still seriously ill".
The OPCW said it received information about the medical conditions of the Skripals and Det Sgt Nick Bailey, it collected their blood samples, and it gathered samples from the site in Salisbury.
Mr Johnson said the UK had invited the OPCW to test the samples "to ensure strict adherence to international chemical weapons protocols".
The OPCW does identify the toxic chemical by its complex formula but only in the classified report that has not been made public.