Five European states have accused Russia of poisoning and killing opposition leader Alexey Navalny with a rare and lethal toxin derived from South American dart frogs, marking a dramatic escalation in international condemnation of Moscow.

In a joint statement issued on Saturday, timed to coincide with the Munich Security Conference, the foreign ministries of the United Kingdom, France, Germany, Sweden and the Netherlands said laboratory analysis of samples taken from Navalny’s body “conclusively confirmed the presence of epibatidine”, a toxin naturally found in poison dart frogs and otherwise absent from Russia. The governments said their findings leave no “innocent explanation” for the chemical’s presence.