"Yulia Navalnaya, the Russian dissident's widow, appeared at a press conference on the sidelines of a security conference in Munich to announce the discovery, flanked by the foreign ministers of the UK, Germany, Sweden and the Netherlands.

The four countries and France have been working together to establish how Mr Navalny, 47, died."

It was not immediately clear how they were able to obtain samples from Mr Navalny's body to test for the toxin, though Ms Navalnaya has previously said they were smuggled out of Russia.

The opposition leader was buried in the suburbs of Moscow in March 2024.

"As a result of the work of the UK, Sweden and other partners, we have confirmed that a deadly toxin was found in Alexei Navalny's body," Ms Cooper told journalists,

"And that toxin has been identified as a toxin that is found in Ecuadorian Dart Frogs."