Russian opposition politician Alexei Navalny in coma after suspected poisoning

Russian opposition politician Alexei Navalny was in a coma in a Siberian hospital on Thursday after drinking a cup of tea that his spokesperson said she believed was laced with poison.

Navalny, 44, was in intensive care and on an artificial lung ventilator, spokesperson Kira Yarmysh said on social media.

A fierce critic of President Vladimir Putin, Navalny started feeling ill when returning to Moscow from Tomsk in Siberia by plane on Wednesday morning, Yarmysh said.

"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," Yarmysh said.

Doctors at the hospital remain tight-lipped about his diagnosis. Anatoliy Kalinichenko, deputy chief doctor of the hospital, told reporters that Navalny was in grave, yet stable condition.

Kalinichenko said doctors are considering a variety of diagnoses, including poisoning, but refused to give details, citing a law preventing doctors from disclosing confidential patient information.

Shadow of Litvinenko, Skripal cases

There is a long history of Kremlin foes being poisoned or falling ill after suspected poisonings.

They include Alexander Litvinenko, who died in London in 2006 after drinking tea laced with polonium-210, and Sergei Skripal, a former double agent who was poisoned with a nerve agent in 2018 in Salisbury, England.

The Kremlin has repeatedly denied involvement in those and other incidents, calling them anti-Russian provocations.

The Kremlin said on Thursday that doctors were doing all they could to help Navalny and that they wished him a speedy recovery.

Kremlin spokesperson Dmitry Peskov said any poisoning would need to be confirmed by laboratory tests.

He said the authorities would be ready to consider a request for Navalny to be treated abroad should one be made.

Yarmysh did not say who she believed may have poisoned Navalny but said police had been called to the hospital.

A regional health ministry spokesperson, Tatyana Shakirova, confirmed that Navalny has been hospitalized in Omsk and said doctors assessed his condition as serious.

"Doctors are doing everything possible to stabilize his condition," she said. "The poisoning version is one of several versions being considered. It's not possible now to say what the reason was."

Navalny, a lawyer and anti-corruption activist, has served many stints in jail in recent years for organizing anti-Kremlin protests and has been physically attacked in the street by pro-government activists.

He has helped investigations into what he has said are outrageous examples of official corruption.

Russia holds regional elections next month and Navalny and his allies have been preparing for them, trying to increase support for candidates they back.

Passenger Pavel Lebedev posted an account of what he saw on social media.

"At the start of the flight he went to the toilet and didn't come back. He started feeling really sick. They struggled to bring him round and he was screaming in pain."

Navalny had drunk a cup of tea at a Tomsk airport cafe before boarding his flight, Yarmysh said. The Interfax news agency quoted the cafe's owners as saying they were checking CCTV cameras to try to establish what had happened.

Emergency landing

Navalny's plane later made an emergency landing in Omsk so that he could be rushed to hospital. Footage posted on social media by a fellow passenger showed a motionless Navalny being stretchered into an ambulance by medics.

S7, the airline he was travelling with, said Navalny had started feeling very ill soon after take-off and the captain had decided to make an emergency landing at a nearby airport.

He had not eaten or drunk anything on board, it said.

WATCH l Navalny suspected he'd been poisoned in 2019:

Yarmysh drew a parallel with an incident last year in which Navalny suffered an acute allergic reaction that one doctor said could have resulted from poisoning with an unknown chemical.

"Obviously the same has been done to him now," Yarmysh said.

The European Court of Human Rights has ruled that Russia's arrests and detention of Navalny in 2012 and 2014 were politically-motivated and violated his human rights, a ruling Moscow called questionable.