British Foreign Secretary Boris Johnson has accused Russia of stockpiling a nerve agent believed to have been used in an attack on a Russian double agent and his daughter in Britain.
Johnson's comments on March 18 came one day ahead of planned visit to Britain by international chemical weapons experts who will probe the poisoning of Sergei Skripal and his daughter Yulia, who were left critically ill on March 4 from a nerve toxin in the southern English city of Salisbury.
Britain has said the toxin used was one of a series of nerve agents that were developed in the late Soviet era and are known by the collective name Novichok. British officials have said Russia was behind Skripal's poisoning, an allegation Moscow rejects.
"We actually have evidence within the last 10 years that Russia has not only been investigating the delivery of nerve agents for the purposes of assassination, but has also been creating and stockpiling Novichok," Johnson told the BBC on March 18.
The Russian ambassador to the European Union, Vladimir Chizhov, told the BBC a day earlier that Russia halted "production of any chemical agents back in 1992" and that a British research facility could have been the source of the toxin used in the poisoning of Skripal.
The poisoning prompted Britain to announce the expulsion of 23 Russian diplomats, with Moscow saying it would reciprocate by expelling the same number of British diplomats.
Johnson told reporters on March 18 that the trail of responsibility for the poisoning leads "leads inexorably to the Kremlin."
The British Foreign Office said in a March 18 statement that investigators from the Organization for the Prohibition of Chemical Weapons would arrive in Britain the following day to begin their probe into the substance used in the poisoning.
Skripal is a former Russian military intelligence officer who betrayed numerous Russian agents to Britain. He and his daughter continue to fight for their lives after they were discovered collapsed on a bench in Salisbury on March 4.