LONDON (AP) — Russian opposition leader Alexei Navalny was poisoned by the Kremlin with a lethal toxin derived from the skin of poison dart frogs, five European countries said Saturday.

The foreign ministries of the U.K., France, Germany, Sweden and the Netherlands said analysis of samples from Navalny, who died two years ago, “have conclusively confirmed the presence of epibatidine.” It is a toxin found in poison dart frogs in South America that is not found naturally in Russia, they said.

The countries said in a joint statement that “Russia had the means, motive and opportunity to administer this poison.” They said they were reporting Russia to the Organization for the Prohibition of Chemical Weapons for a breach of the Chemical Weapons Convention.

British Foreign Secretary Yvette Cooper said "Russia saw Navalny as a threat. By using this form of poison the Russian state demonstrated the despicable tools it has at its disposal and the overwhelming fear it has of political opposition.”

Navalny, who crusaded against official corruption and staged massive anti-Kremlin protests as President Vladimir Putin’s fiercest foe, died in the Arctic penal colony in February 2024. He was serving a 19-year sentence that he believed to be politically motivated.

Navalny’s widow, Yulia Navalnaya, said last year that two independent labs had found that her husband was poisoned shortly before he died. Navalnaya has repeatedly blamed Putin for Navalny’s death, something Russian officials have vehemently denied.

Navalnaya said Saturday that she had been “certain from the first day” that her husband had been poisoned, “but now there is proof.”

“Putin killed Alexei with chemical weapon,” she wrote on social network X, calling Putin “a murderer” who “must be held accountable.”

Russian authorities said that the politician became ill after a walk and died from natural causes.

In 2020, Navalny was poisoned with a nerve agent attack he blamed on the Kremlin, which always denied involvement. His family and allies fought to have him flown to Germany for treatment and recovery. Five months later, he returned to Russia, where he was immediately arrested and imprisoned for the last three years of his life.