Russian opposition leader Alexei Navalny was admitted to a Siberian hospital Thursday (August 20) and is now in serious condition.
That's according to Navalny's spokeswoman, who suspects he was deliberately poisoned.
Navalny, a lawyer and an anti-corruption activist, is a fierce critic of President Vladimir Putin.
He's helped release high-impact investigations into what he's claimed to be outrageous examples of official corruption--and has served several stints in jail in recent years for organising anti-Kremlin protests.
Navalny's spokeswoman said he started feeling ill when flying back to Moscow from Siberia on Wednesday morning.
He reportedly drank tea at a cafe at Tomsk airport before boarding his flight, which later made an emergency landing so that he could be rushed to the hospital.
His spokeswoman added that the 44-year-old Navalny is now unconscious, in intensive care and on an artificial lung ventilator.
She did not say who may have poisoned Navalny, but said that police have now been called to the hospital.
Navalny and his allies had been busy preparing for Russia's regional elections next month, trying to increase support for candidates which they back.