Alexei Navalny was possibly poisoned.

Tests conducted on Russian dissident Alexei Navalny at a German hospital indicate that he was probably poisoned.

Tests conducted on Russian dissident Alexei Navalny at a German hospital indicate that he was probably poisoned. Berlin’s Charité hospital said that they have found the presence of “cholinesterase inhibitors” in his system. Cholinesterase inhibitors are a broad range of substances that are found in several drugs, but also pesticides and nerve agents. However, at the moment, doctors at Charite said the specific substance to which Navalny was exposed is not yet known.

Navalny remained in critical but stable condition at the Berlin hospital, with special protection details on hand to ensure his safety. The Associated Press reported that Navalny’s supporters believe that tea he drank was laced with poison, and that the Kremlin is behind both his illness and a delay in transferring him to Germany.

Russian doctors had previously said that tests had shown no traces of poison in his system. The Kremlin hasn’t yet commented on the new report.

Navalny, a politician and corruption investigator who is one of Russian President Vladimir Putin’s fiercest critics, fell ill on a flight back to Moscow from Siberia on August 20 and was taken to the hospital in the city of Omsk after the plane made an emergency landing.