Russian opposition leader Alexei Navalny was killed by poisoning carried out by the Kremlin using a deadly toxin sourced from the skin of poison dart frogs, five European nations alleged Saturday.

Foreign ministries from the U.K., France, Germany, Sweden and the Netherlands said testing conducted on samples taken from Navalny, who died two years ago, “have conclusively confirmed the presence of epibatidine.”

They described the substance as a toxin found in South American poison dart frogs and noted that it does not occur naturally in Russia.

In a joint statement, the countries said “Russia had the means, motive and opportunity to administer this poison.” They added that they are formally reporting Moscow to the Organisation for the Prohibition of Chemical Weapons for violating the Chemical Weapons Convention.