Russian opposition leader Alexei Navalny was hospitalized with signs of poisoning. Navalny felt sick on the plane he was flying to the city of Tomsk. His rapidly deteriorating condition forced the captain to do an emergency landing in Omsk, Unian report.

“We assume that Alexei was poisoned with something poured into his tea. It was the only thing he drank this morning. Doctors say the toxin absorbed faster through hot liquid. Now Alexei is unconscious,” said his press secretary Kira Yarmysh.

Alexey Navalny is a vocal critic of Russian President Vladimir Putin. He has produced multiple probes into local corruption in Russian regions. Navalny admitted that the Russian military were fighting in Donbas, and promised to withdraw troops once he becomes president.