Kremlin critic Alexei Navalny said on Monday he had tricked a Russian secret agent into disclosing details of the botched plot to kill him and had been told that poison had been placed in his underpants.

Navalny, one of President Vladimir Putin’s most outspoken critics, was airlifted to Germany for treatment in August after collapsing on a plane in Russia. Germany has said he was poisoned with a Soviet-style Novichok nerve agent in an attempt to murder him, an assertion many Western nations accept.