Russian opposition leader Alexei Navalny has been hospitalized and is now unconscious suffering from suspected poisoning, his spokeswoman has said.

Alexei Navalny fell ill during a flight and the plane made an emergency landing in Omsk, where doctors said he was in a coma and they were trying to save his life.

The anti-corruption campaigner’s team suspects something was put in his tea at an airport cafe.

The Kremlin said that it wished Alexei Navalny a “speedy recovery”.

Alexei Navalny, 44, has for years been among President Vladimir Putin’s staunchest critics.

In June, the opposition leader described a vote on constitutional reforms as a “coup” and a “violation of the constitution”. The reforms allow President Putin to serve another two terms in office, after the four terms he has already had.

Kira Yarmysh, the press secretary for the Anti-Corruption Foundation, which Mr Navalny founded in 2011, tweeted: “This morning Navalny was returning to Moscow from Tomsk.

“During the flight, he felt ill. The plane made an urgent landing in Omsk. Alexei has toxic poisoning.”

She added: “We suspect that Alexei was poisoned by something mixed into [his] tea. It was the only thing he drank since morning.

“Doctors are saying that the toxic agent absorbed faster through the hot liquid. Right now Alexei is unconscious.”

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Kira Yarmysh said later that Alexei Navalny was on a ventilator and in a coma, and that the hospital was now full of police officers. All of his belongings were being confiscated, she added.

She also said that doctors were initially ready to share any information but then they later claimed the toxicology tests had been delayed and were “clearly playing for time, and not saying what they know”.

Diagnosis would be “towards evening”, Kira Yarmysh was told.

BothAlexei Navalny’s wife, Yulia Navalnaya, and doctor, Anastasia Vasilyeva, have arrived at the hospital.

Yulia Navalnaya was initially denied access to her husband because authorities said the patient had not agreed to the visit, Kira Yarmysh said, although she was later allowed on to the ward.

Dr. Anastasia Vasilyeva said they were seeking to transfer the opposition leader to a specialist poison control center in Europe, but hospital doctors were refusing to provide records of his condition.

The Tass news agency quoted one source at the Omsk Emergency Hospital as saying: “Alexei Anatolyevich Navalny, born in 1976. Poisoning intensive care.”

However, the deputy head physician of the hospital later told media that it was not certain Alexei Navalny had been poisoned, although poisoning was “naturally” one of the diagnoses being considered.

Anatoly Kalinichenko said that doctors were “genuinely trying to save [Alexei Navalny’s] life”.

Kremlin spokesman Dmitry Peskov later said it wished the critic a speedy recovery – as it would all citizens in such circumstances – and that the authorities would consider approving treatment abroad if it were requested.

Video footage on social media shows Alexei Navalny being taken on a stretcher to an ambulance on the airport runway.

Other disturbing video appears to show a stricken Navalny in pain on the flight.

Another photograph on social media purports to show him drinking from a cup at a Tomsk airport cafe.

The Interfax agency said the cafe owners were checking CCTV to see if it could provide any evidence.

Alexei Navalny made a name for himself by exposing official corruption, labeling Vladimir Putin’s United Russia as “the party of crooks and thieves”, and has served several jail terms.