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.
The group, the Organization for the Prohibition of Chemical Weapons, released a report saying that its laboratory analysis of "environmental and biomedical samples" that its experts had collected "confirm the findings of United Kingdom relating to the identity of the toxic chemical".
However a "combination of credible open-source reporting and intelligence" showed that in the 1980s the Soviet Union developed a "fourth generation" class of nerve agents known as Novichoks. "It is now up to Russian Federation to finally play a constructive role and answer the open questions", he said.
He said the watchdog's findings were based on testing in four independent, highly reputable laboratories around the world, all of which returned the same "conclusive" results.
Russian Federation strongly denies involvement in the attack, which has sparked an worldwide row resulting in the expulsions of diplomats from all sides.
The U.K. has called a meeting of the OPCW's executive council for April 18 to discuss next steps, Johnson said.
A British police officer was also taken ill after attending the scene.British Foreign Secretary Boris Johnson hailed the chemical watchdog's findings.
British Foreign Secretary Boris Johnson said on Friday (Thursday local time) the findings show "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". "The use of weapons of this kind can never be justified, and must be ended", he said. She also said she would give interviews to the media in time, but asked the press to have patience while she recovers.
"While we feel rightly outraged at this act, I have seen no sense that the city wishes anything but friendship with the Russian people and better relations between our governments".
Doctors treating the two victims of last month's poisoning attack in Salisbury England, have confirmed that one of the victims Yulia Skripal has been released from hospital. In a diplomatic row that followed a number of Western countries "in a gesture of solidarity" with Britain expelled Russian diplomats.
Russian Foreign Ministry Spokeswoman Zakharova said: "Even if it's Novichok, about 20 countries produced it".
Police who launched an investigation into the attempted murders of Mr Skripal and his daughter, who was visiting him from Russian Federation, believe that the pair first came into contact with the novichok nerve agent at his home in Salisbury, Wiltshire.
"We can not be sure that Yulia's refusal to see us is genuine".