The United Kingdom has repeatedly refused to share samples or answer Russia’s questions about a nerve agent called A234, but Vladimir Uglev, a former Soviet scientist who claims to have created it, told BBC he had been sent "spectrum data" on the toxin.
"This is quite an extraordinary statement. It essentially means that a private citizen has been provided with the information that the Russian Side has not been able to obtain from the British authorities for weeks," the mission said in a statement.
British investigators reportedly believe that the nerve agent was used last month to poison former Russian spy Sergei Skripal and his daughter Yulia at their Salisbury home. The British government has blamed Russia for the chemical attack but has not provided any proof. Russia denies the claim.