Britain and several European allies have said Russian opposition leader Alexei Navalny was killed using a rare poison made from a dart frog toxin, blaming the Russian state for his death.

In a joint statement issued two years after Navalny died in a Siberian penal colony, the UK, Sweden, France, Germany and the Netherlands said tests found traces of epibatidine in samples taken from his body. The toxin has no natural link to Russia and there is no innocent explanation for its presence, the UK Foreign Office said.

UK Foreign Secretary Yvette Cooper said only the Russian government had the means, motive and opportunity to use such a lethal substance against Navalny during his imprisonment. She made the remarks while speaking at the Munich Security Conference.

The allies said epibatidine is found naturally only in certain wild dart frogs in South America. It is not produced by frogs in captivity and does not occur naturally in Russia. They said the Russian state should be held responsible for Navalny’s death.

The UK has informed the Organisation for the Prohibition of Chemical Weapons about what it described as a possible breach of the Chemical Weapons Convention by Russia.

UK Prime Minister Keir Starmer praised Navalny’s courage and said his fight to expose the truth left a lasting legacy. France’s Foreign Minister Jean Noël Barrot also paid tribute, saying Navalny was killed for his struggle for a free and democratic Russia.

Navalny, a leading anti corruption campaigner and fierce critic of the Kremlin, died in custody on Feb 16, 2024, at the age of 47. He had been jailed for several years on charges widely seen by critics as politically motivated.

His wife, Yulia Navalnaya, has long said her husband was poisoned in prison. Reacting to the latest findings, she said she was convinced from the first day that he had been poisoned and thanked European states for uncovering the truth after detailed work.

The Kremlin has not commented on the allegations. Russian President Vladimir Putin previously avoided mentioning Navalny by name and gave only a brief remark after his death.

Experts say epibatidine is an extremely rare neurotoxin and far stronger than morphine. It can affect the nervous system and lead to paralysis, breathing failure and death.

With inputs from BBC