Russia and Britain faced off yesterday trading accusations at a tense meeting of the world's chemical weapons watchdog, as Moscow accused British and U.S. secret services of being behind the poisoning of a former Russian double agent.

London slammed as "perverse" a Russian proposal for a joint probe into the poisoning of former Russian spy Sergei Skripal and his daughter Yulia with a nerve agent, dismissing it as a "diversionary tactic." But Russian officials hit back that accusations of Moscow engineering the attack were a "grotesque provocation… crudely concocted by the British and American security services."

At Moscow's request, the Organization for the Prohibition of Chemical Weapons (OPCW) held a special session yesterday in The Hague on the Salisbury poisoning. The OPCW's executive council has 41 members, including Russia and Britain. Any decisions must be approved by two thirds of members, which is generally difficult to achieve.

"We have raised 20 questions for discussion [at the meeting]. I hope that during this discussion a final line on what has happened will be drawn," Russian President Vladimir Putin told a news conference during a visit to Ankara, Reuters reported.

Moscow has said it wants to take part in the official British investigation into the poisoning.

"We are interested in a full-fledged investigation. We want to be allowed into this investigation and we count on receiving relevant materials as the issue involves citizens of the Russian Federation," Putin said.

Britain's defense laboratory acknowledged Tuesday it had not tracked down the source of the nerve agent that poisoned Skripal, a statement the Kremlin said proved that British accusations of Moscow's involvement were baseless.

Scientists at the U.K's Porton Down lab previously identified the poison as a Soviet-developed type of nerve agent known as novichok. The British government has said the only plausible explanation was that it came from Russia and blamed Russia for the attack on the former double agent and his adult daughter.

Porton Down CEO Gary Aitkenhead said that scientists at the lab "have not verified the precise source, but we provided the scientific information to the government who have then used a number of other sources to piece together the conclusions that they have come to," as reported by The Associated Press (AP).

Britain has blamed Russia for the poisoning of Skripal and his daughter with a military-grade nerve agent in the English city of Salisbury on March 4. Moscow denies any involvement and has accused London of whipping up anti-Russian hysteria in the West.

The Skripal case has plunged West-Russian relations into their worst crisis since the Cold War, with Britain and its allies expelling around 130 Russian diplomats and Moscow responding with its own expulsions.