Russian opposition leader Alexei Navalny, who died in 2024 under murky circumstances in prison, was "poisoned" with a "rare toxin," epibatidine, by Moscow, five European countries, including the United Kingdom, accused on Saturday.

"The United Kingdom, Sweden, France, Germany and the Netherlands are convinced that Alexei Navalny was poisoned with a lethal toxin," the countries said in a joint statement, issued on the sidelines of the Munich Security Conference.

"Only the Russian state had the means, the motive and the opportunity to use this deadly toxin to target Navalny during his imprisonment in a Russian penal colony in Siberia," the statement added, saying it held Moscow "responsible for his death."

Immediately after this announcement, his widow Yulia Navalnaya declared that his "assassination" was now "proven by science".

"Two years ago (...) I came on stage and said 'Vladimir Putin killed my husband' (...) And today those words have become a fact proven by science," she said.

European countries explain that "constant and collaborative work has confirmed, through laboratory analyses, that the deadly toxin present in the skin of Ecuadorian dart frogs (epibatidine) was found in samples taken from the body of Alexei Navalny."

They add that this toxin "very likely caused his death".

They wrote to the Organisation for the Prohibition of Chemical Weapons (OPCW) to report the poisoning. When contacted by AFP, the OPCW did not immediately respond.

Moscow has never admitted that Mr. Navalny was the target of an assassination attempt.

At this stage, the Kremlin has not commented on the accusation from the five European countries.

Russian Foreign Ministry spokeswoman Maria Zakharova, quoted Saturday by the state news agency TASS, said that Moscow would react after reviewing the report and called "all these statements and claims informational chaos aimed at diverting attention from the real problems of the West."

The Russian embassy in London denounced it as a "political stunt" on its Telegram page.

- "Barbaric Project" -

Charismatic anti-corruption activist and fierce opponent of the Russian invasion of Ukraine launched in 2022, Alexei Navalny died at the age of 47 in unclear circumstances in a penal colony in the Arctic, while serving a 19-year prison sentence for charges he denounced as political.

After his death, the authorities refused for several days to release his body to his family, which aroused suspicion among his supporters. They accused the government of having "killed" him and of trying to cover up his murder.

"Today, alongside his widow, the United Kingdom is highlighting the Kremlin's barbaric plan to silence his voice," she added.

French Foreign Minister Jean-Noel Barrot also commented on the subject on the social network X.

"We now know that Vladimir Putin is prepared to use bacteriological weapons against his own people to maintain his grip on power," he said, adding that France "pays tribute to this figure of the opposition, killed for his fight for a free and democratic Russia."

In their statement, the five countries said they were "concerned that Russia has not destroyed all of its chemical weapons," accusing Moscow of violating the Chemical Weapons Convention.

Mr. Navalny had already been poisoned with the nerve agent Novichok in 2020 while campaigning in Siberia. He and his supporters blamed the Kremlin, which has always denied it.

Transferred in a coma to Germany for treatment, he chose to return to Russia and was imprisoned for "extremism".

They also mention the death of a British woman in 2018, a collateral victim of the Novichok poisoning of former Russian double agent Sergei Skripal.

An independent investigation, whose findings were released in December, highlighted the "moral responsibility" of President Vladimir Putin in the death of this 44-year-old mother.