The substance that killed a woman in England in June was the same Novichok nerve agent that poisoned a former Russian agent and his daughter in May, the world's chemical-weapons watchdog has confirmed.
The Organization for the Prohibition of Chemical Weapons (OPCW) said on September 4 that laboratory tests of samples collected by its team "confirm the findings of the United Kingdom relating to the identity of the toxic chemical."
However, it was not possible to conclude whether the nerve agent used in the May and June incidents was from the same batch, the OPCW said.
"The recklessness of the Russian state in bringing a nerve agent in to the U.K., and total disregard for the safety of the public, is appalling and irresponsible," British Foreign Secretary Jeremy Hunt said.
Moscow has denied any involvement in the poisonings.
On June 30, two people collapsed in a house in Amesbury, near the English town of Salisbury where Sergei and Yulia Skripal were poisoned with Novichok in March.
Dawn Sturgess died in a hospital in July, while her partner, Charlie Rowley, later recovered.
Police said they were exposed after handling what they believed to be perfume.
The Skripals were found unconscious on March 4 on a bench in Salisbury.
They were seriously ill but later made a full recovery after spending several weeks in a hospital.
British officials said the two were poisoned with Novichok, a military-grade chemical weapon that was developed in the Soviet Union, and blamed Russian President Vladimir Putin's government for the attack.
U.S. sanctions against Russia over the March poisoning went into effect on August 27, targeting foreign aid, the sale of defense and security goods, and U.S. government loans for exports to Russia.
Relations between Moscow and the West have deteriorated to a post-Cold War low over issues including Russia's seizure of Crimea in 2014, its role in wars in Syria and eastern Ukraine, and its alleged election meddling in the United States and Europe.