Laboratory tests by a chemical weapons watchdog confirmed British conclusions that two people in Amesbury, southwest England, were exposed to a Novichok-type nerve agent, it said on Tuesday.
The Organisation for the Prohibition of Chemical Weapons (OPCW) said analysis by designated laboratories of samples collected by its team "confirm the findings of the United Kingdom relating to the identity of the toxic chemical."
Dawn Sturgess, 44, died after she and her partner were exposed to the toxin near the city of Salisbury where Russian double agent Sergei Skripal and his daughter Yulia were struck down with the same poison in March.
The OPCW said "it is also the same toxic chemical that was found in the biomedical and environmental samples relating to the poisoning of Sergei Skripal."
The U.K. has accused Russia, which developed the toxic agent in the Soviet Union era, of poisoning the Skripals. Moscow denies all involvement.
Britain is ready to ask Russia to extradite two men it suspects of carrying out the nerve agent attack on Skripal.