The German government has said Russian opposition leader Alexei Navalny was poisoned with a chemical nerve agent while in Russia.

In a statement on Wednesday, two weeks after Navalny suddenly fell ill during a flight in Russia, the German government said a special military laboratory carried out a toxicological test on the Kremlin’s critic, who is undergoing treatment at a Berlin hospital.

The statement said tests confirmed the nerve agent used comes from the Novichok family — the type of nerve agent that was used in the poisoning of Russian ex-spy Sergei Skripal and his daughter in the U.K. two and a half years ago.

“Thereby the unequivocal evidence of a chemical nerve agent of the Novichok group was detected,” the statement said.

“It is a startling event that Alexei Navalny was the victim of an attack with a chemical nerve agent in Russia,” the statement added.

“The federal government condemns this attack in the strongest possible terms. The Russian government is urged to provide an explanation on the incident.”

This is a developing story — check back here for updates.