Alexei Navalny, 44 is in critical condition and has been rushed to hospital in intensive care in the Siberian city of Omsk, according to the TASS news agency. The politician’s spokeswoman, Kira Yarmysh, said Mr Navalny was in intensive care after showing signs of being poisoned.
Ms Yarmysh said Mr Navalny, 44, is on an artificial lung ventilator.
She posted on social media: “We assume that Alexei was poisoned with something mixed into his tea. It was the only thing that he drank in the morning.
“Doctors say the toxin was absorbed faster through the hot liquid. Alexei is now unconscious.
She said Mr Navalny, a fierce critic of Russian President Vladimir Putin, had started feeling ill when returning to Moscow from Tomsk in Siberia by plane on Wednesday morning.
He had drunk tea at a cafe at Tomsk airport before boarding his flight. The cafe owners are said to be checking CCTV cameras to try to establish what had happened, Interfax news agency reported.
Ms Yarmysh said the activist’s plane later made an emergency landing in Omsk so he could be rushed to hospital.
The head doctor at a hospital in Omsk confirmed Mr Navalny had been admitted there and he was in a serious condition, the TASS news agency reported.
Ms Yarmysh drew a parallel with an incident last year in which Mr Navalny suffered an acute allergic reaction that one doctor said could have resulted from poisoning with an unknown chemical.
It was during the time Mr Navalny was serving a 30-day jail sentence after calling for unauthorised protests.
Russia holds regional elections next month and Mr Navalny and his allies have been preparing for them, trying to increase support for candidates which they back.
The European Court of Human Rights has ruled that Russia’s arrests and detention of Mr Navalny in 2012 and 2014 were politically-motivated and violated his human rights, a ruling Moscow called questionable.
