Britain has demanded Russia to provide details about the Novichok nerve agent attack on a former double agent and his daughter, after two British citizens were struck down with the same poison in March.
Russia has denied any involvement in the March incident and suggested the British security services have carried out the attack only to stoke anti-Moscow hysteria.
British officials have hypothesised the latest pair may have been contaminated in a different location from areas visited by the former Russian agent and his daughter.