The world's chemical watchdog is to meet behind closed doors Wednesday, after a British laboratory said it had not proved that Russia manufactured a deadly nerve agent used to poison a former Russian spy. The talks at the Organisation for the Prohibition of Chemical Weapons (OPCW) have been requested by Moscow which said it wanted to "address the situation around the allegations... in regards to the incident in Salisbury." "We hope to discuss the whole matter and call on Britain to provide every possible element of evidence they might have in their hands," Russia's ambassador to Ireland, Yury Filatov, told reporters. On Tuesday, the British military facility analysing the nerve agent used on former Russian double agent Sergei Skripal and his daughter Yulia, said it was not in a position to say where the substance had originated. Skripal, who has lived in Britain since a spy swap in 2010, and his daughter have been in hospital since the March 4 poisoning that London and its major Western allies have blamed on Russia. The 41 member states of the OPCW's executive council are to convene at 10:00 am (0800 GMT) at the organisation's headquarters in The Hague. The meeting comes after Moscow also received and analysed samples of the Novichok agent used in the attack. "Russia is interested in establishing the whole truth of the matter," Filatov said. But Britain's foreign ministry accused Russia of requesting the meeting to undermine the OPCW's investigation. "This Russian initiative is yet again another diversionary tactic, intended to undermine the work of the OPCW in reaching a conclusion," the ministry said in a statement. "Of course, there is no requirement in the Chemical Weapons Convention for the victim of a chemical weapons attack to engage in a joint investigation with the likely perpetrator," it said. - 'Source unidentified' - Gary Aitkenhead, chief executive of the Porton Down defence laboratory, told Britain's Sky News that analysts had identified the substance as military-grade Novichok, the word used for a category of nerve agents developed in Soviet times. But he added: "We have not identified the precise source." "It is our job to provide the scientific evidence of what this particular nerve agent is, we identified that it is from this particular family and that it is a military grade, but it is not our job to say where it was manufactured," Aitkenhead said. "Extremely sophisticated methods" were needed to create the nerve agent, he said, adding that was "something only in the capabilities of a state actor" Following his remarks, a British government spokesperson said Porton Down's identification of Novichok was "only one part of the intelligence picture". "This includes our knowledge that within the last decade, Russia has investigated ways of delivering nerve agents probably for assassination –- and as part of this programme has produced and stockpiled small quantities of Novichok; Russia's record of conducting state-sponsored assassinations; and our assessment that Russia views former intelligence officers as targets," it added. - 'Anti-Russian campaign' - The first use of chemical weapons in Europe since World War II has chilled Moscow's relations with the West, as both sides have expelled scores of diplomats. Britain has also suspended high-level diplomatic contact with Moscow. Moscow has denied any involvement in the incident, with Russian President Vladimir Putin saying late Tuesday he hoped the OPCW meeting would put a "full stop" to the issue. Putin added he had been informed that the British military could not prove the substance was made in Russia. An "anti-Russian campaign" had been started with surprising speed, Putin said, reiterating Moscow's claim that it should be allowed to take part in the investigation.