Skripal and his daughter were poisoned on March 4 in the English city of Salisbury.
British authorities concluded that the chemical agent used was military-grade novichok, a chemical weapon developed by the Soviet Union during the Cold War.
Tests carried out by experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) showed the nerve agent was found in environmental samples collected in Salisbury.
Western leaders said they agreed with Britain's assessment that it was highly likely Russian Federation was responsible for the attack.
"This finding massively increases the pressure on Moscow to fully explain the exact course of events and background of the first nerve agent attack on European soil", he said.
But it did confirm Britain's analysis about the substance that had been used.
Blood samples "confirm the findings of the United Kingdom relating to the identity of the toxic chemical", according to a summary of the Hague-based group's report released in London.
Responding to the report, Britain called a session of the OPCW to discuss next steps.
Britain and its allies point the finger at Moscow, sparking an global row that led to the mass expulsion of diplomats on both sides. Moscow has denied any involvement.
Russian Federation said it would not believe any conclusions about the poisoning unless it was given access to the investigation, and said the allegations were part of a British operation to discredit Russian Federation.
The OPCW report comes as Yulia turned down help from the Russian embassy in a statement issued through Scotland Yard yesterday to say that she was "safe" and trying to come to terms with her new life.
Britain says scientific analysis of the poison is only one of the factors that has led it to blame Russian Federation.
"In the interest of transparency, and because unlike the Russians we have nothing to hide, we have asked the OPCW to publish the executive summary for all to see", Mr Johnson said in a statement.
He said: 'There can be no doubt what was used and there remains no alternative explanation about who was responsible - only Russian Federation has the means, motive and record'. This has also prevented it from acting on the use of chemical weapons in Syria.