Five European countries say tests confirm Russian opposition leader Alexei Navalny was poisoned with a lethal toxin found in poison frogs, and they blame the Russian state.

FILE - Russian opposition leader Alexei Navalny speaks to the media in front of security officers standing guard at the Foundation for Fighting Corruption office in Moscow, Russia, Thursday, Dec. 26, 2019. (AP Photo/Alexander Zemlianichenko, File)via Associated Press

Russian opposition leader Alexei Navalny was poisoned by the Kremlin with a rare and lethal toxin found in 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 taken from Navalny`s body "conclusively confirmed the presence of epibatidine." It is a neurotoxin found in the skin of 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.

They made the announcement as Navalny`s widow Yulia Navalnaya attended the Munich Security Conference in Germany as the second anniversary of Navalny`s death approaches.

Navalny, who crusaded against official corruption and staged massive anti-Kremlin protests as President Vladimir Putin`s fiercest foe, died in an Arctic penal colony on Feb. 16, 2024. He was serving a 19-year sentence that he believed to be politically motivated.

"Russia saw Navalny as a threat," British Foreign Secretary Yvette Cooper said. "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`s widow, 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.

Epibatidine is found naturally in dart frogs in the wild, and can also be manufactured in a lab, which European scientists suspect was the case with the substance used on Navalny. It works on the body in a similar way to nerve agents, causing shortness of breath, convulsions, seizures, a slowed heart rate and ultimately death.

Navalny was the target of an earlier poisoning in 2020, with a nerve agent in an 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.

The U.K. has accused Russia of repeatedly flouting international bans on chemical and biological weapons. It has accused the Kremlin of carrying out a 2018 attack in the English city of Salisbury that targeted a former Russian intelligence officer, Sergei Skripal, with the nerve agent Novichok. A British inquiry concluded that the attack "must have been authorized at the highest level, by President Putin."

The Kremlin has denied involvement.