The U.K. has said its experts from the Porton Down defense research center concluded that the military-grade nerve agent that was used in the attack belonged to a Russia-developed chemical weapon group called Novichok.
The team "notes that the toxic chemical was of high purity", it added, lending support to Britain's claim that the nerve agent was manufactured with a degree of expertise and sophistication strongly indicating that a national government was responsible.
Results of the OPCW's analysis "confirm the findings of the United Kingdom relating to the identity of the toxic chemical that was used in Salisbury", the organization said in a statement on Thursday.
Russian Federation has denied all involvement of the attack, arguing Britain has not provided any evidence for its assertion.
The OPCW laboratories tests' - the details of which were kept confidential - findings about the chemical's purity supports the British Government's assertion that a state was involved.
Johnson says "there can be no doubt what was used and there remains no alternative explanation about who was responsible - only Russian Federation has the means the motive and record".
U.K. Foreign Secretary Boris Johnson said in a statement that the OPCW's conclusion showed "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 OPCW did not explicitly name Novichok in its published summary, say where the poison may have come from or assign blame for the attack.
Russia, which denies it was behind the attack in Salisbury, called the allegations an "anti-Russian campaign".
Prime Minister Theresa May's government has said Russian Federation was known to have used Novichok, and pointed to the country's pattern of "reckless behavior", including the annexation of Crimea.
Despite initial fears that they would not survive, Yulia Skripal was released from hospital to an undisclosed location earlier this week, while her father is said to be improving rapidly. Yulia was discharged from Salisbury District Hospital this Monday, while her father is in a stable condition and recovering slowly. Skripal, a former Russian intelligence officer who became a British mole, had been swapped for the "Anna Chapman" spy ring in the US; Russia also added three other Russian turncoats, including the man who blew Chapman's cover. "The use of weapons of this kind can never be justified, and must be ended", he said.
OPCW analysts, based in The Hague, took blood samples from the Skripals as they were treated in Salisbury Hospital after the March 4 poisoning. That was an apparent reference to a cousin in Russia, Viktoria Skripal, who has repeatedly popped up in interviews with official Russian media and has offered to travel to Britain to bring her cousin home.
British authorities "must urgently provide tangible evidence that Yulia is alright and not deprived of her freedom", the embassy said in a statement.
"The document only strengthens suspicions that we are dealing with a forcible isolation of the Russian citizen", the Russian Embassy said in its statement.