Navalny, 44, started feeling unwell while on a return flight to Moscow from the Siberian city of Tomsk, his spokeswoman Kira Yarmysh, said on Twitter. The plane later made an urgent landing in Omsk, she added.
He only drank black tea in an airport cafe before takeoff, Yarmysh told Russian radio station Echo of Moscow.
“We assume that Alexey was poisoned with something mixed into the tea. It was the only thing that he drank in the morning. Doctors say the toxin was absorbed faster through the hot liquid,” Yarmysh tweeted.
Loud groaning can be heard in video footage apparently filmed on the flight taken by Navalny, which was shared on the Baza Telegram channel. More video apparently filmed through the airplane window shows an immobile man being taken by wheeled stretcher to a waiting ambulance.
Navalny has been admitted to the acute poisoning unit of Omsk emergency hospital No. 1 and is in a “serious condition,” hospital head physician Alexander Murakhovsky said, according to Russian state news agency TASS.
The hospital’s deputy head physician, Anatoly Kalinichenko, speaking to local journalists, later confirmed that Navalny was still in the hospital in a serious condition. He was on a ventilator but was stable, the physician said.
Asked by a reporter if Navalny had been poisoned, Kalinichenko said: “Naturally, poisoning is considered as one of the possible reasons for the deterioration of his state. But apart from this, this could be a number of conditions that started acutely and led to the same clinical reactions. We are working on all of them: excluding, confirming.”
Kalinichenko said he believed doctors would have a diagnosis later Thursday. In the meantime, Navalny’s symptoms are being treated, he said.
In an earlier tweet, Yarmysh said the intensive care unit was full of police officers.
“They try to get an explanation from the doctor. The doctor saw me in the distance in the corridor, said that ‘some things are confidential’ and took the police to another room,” Yarmysh said.
“The evasive reaction of doctors only confirms that this is poisoning,” Yarmysh added.
Navalny’s attending physician, Anastasia Vasilyeva, said she had flown to Omsk after hearing the news of his hospitalization but had not been allowed to see Navalny or been given any information regarding his condition.
“We ask for help from the Ministry of Health and other officials to obtain documents [on Navalny’s condition], to determine the treatment and the need to transfer him to Moscow or abroad,” she posted on her Twitter account.
Yarmysh tweeted that Navalny’s wife, Yulia Navalnaya, also had not been not allowed to see him in the intensive care unit on the grounds that “the patient did not give his consent to a visit.”
Kremlin spokesman Dmitry Peskov said the Kremlin was aware of media reports about Navalny’s hospitalization.
“We know that he is in a serious condition. Doctors are now doing what is necessary. In Omsk, the best doctors are involved in this case,” he said on a regular conference call with journalists.
“They hold consultations with specialists from Moscow. Of course, like for any citizen of our country, we wish him a speedy recovery.”
Peskov said the Kremlin would be ready to consider any request for assistance from Navalny’s team should they ask about taking him abroad for treatment.
Asked if the Kremlin knows whether Navalny was poisoned with a hallucinogen, Peskov said the results of tests were still awaited.
“So far, as far as we know, there are no analysis results, so [these] are only assumptions about whether it was poisoning or not. This must be confirmed by laboratory tests,” Peskov said.
Lithuanian Foreign Minister Linas Linkevicius described the reports of Navalny’s suspected poisoning as “very worrying” on Twitter.
“If confirmed, those responsible must face consequences. Closely following the situation, wishing him strength and speedy recovery,” he said.
UK Foreign Secretary Dominic Raab tweeted that he was “deeply concerned” by reports that Navalny “has been poisoned on a flight to Moscow and is now in a coma in intensive care.”
More details are emerging of the events leading up to Navalny’s hospitalization.
Yarmysh told Russian media outlet Mediazona that Navalny had shown no signs of illness until after they had taken off from Tomsk.
“He said that he was not feeling well and asked me for a napkin, he had perspiration,” Yarmysh told Echo. “He asked me to talk to him because he wanted to concentrate on the sound of the voice. I talked to him, after which a trolley with water came up to us — I asked if water would help him; he said no. Then he went to the toilet, after which he lost consciousness.”
S7 Airlines told TASS that the opposition leader “did not eat or drink anything” during the flight.
“Soon after the takeoff of flight S7 2614 Tomsk-Moscow, the state of health of one of the passengers, Alexey Navalny, sharply deteriorated,” the company said.
According to S7, the crew “worked quickly and strictly in accordance with the procedures.” The flight attendants immediately reported the incident to the aircraft commander who landed the airliner at the nearest airport.
After refueling, the plane went on to Moscow but two passengers who were flying with Navalny stayed in Omsk, TASS said.
Lawyers representing Navalny’s Anti-Corruption Fund (FBK) will submit an application to Russia’s Investigation Committee demanding that it open a criminal investigation into his alleged poisoning, FBK lawyer Vyacheslav Gimadi wrote on Twitter.
“There is no doubt that Navalny was poisoned for his political position and activities,” Gimadi said.
Navalny previously suggested he might have been poisoned in July last year, while he was being held in police custody and suffered a mysterious allergic reaction. After receiving medical assistance, he was sent back to detention.
Doctors did not find any signs of poisoning after doing analysis on the opposition leader, TASS reported last year.
In an interview with CNN’s Matthew Chance in 2018, Navalny said speaking out in Russia entailed a serious risk.
“Anyone who is engaged in opposition activities in Russia can be arrested or killed,” he said. “This thought gives me no pleasure or joy, I assure you, but it is a simple choice: you can be silent or you can speak. Taking into account all the risks, I continue my work.”
Other Kremlin critics or opponents have been involved in apparent poisoning incidents or suffered mysterious deaths.
Prominent investigative journalist Anna Politkovskaya, who was assassinated as she returned to her Moscow home in 2006, claimed in September 2004 that she had been poisoned with tea on a flight to Rostov as she attempted to reach Beslan, North Ossetia, to report on the school hostage crisis there.
Writing in The Guardian, she described how 10 minutes after drinking the tea, “I realise that I have to call the air stewardess as I am rapidly losing consciousness.” Politkovskaya says she was taken to a hospital, where she writes that a nurse told her: “My dear, they tried to poison you.”
A British inquiry found that two Russian agents poisoned ex-Russian spy Alexander Litvinenko at a London hotel bar in 2006 by spiking his tea with highly radioactive polonium-210. From his deathbed, Litvinenko insisted that Putin and the Kremlin were responsible for what happened. Moscow dismissed the inquiry as politically motivated.
In March 2018, former Russian agent Sergei Skripal and his daughter Yulia were poisoned in the English city of Salisbury in what British authorities assessed to be a nerve agent attack carried out by Russian military intelligence officers. Russia has denied any role in the poisoning.
Vladimir Kara-Murza, a vocal critic of Putin, said he was poisoned in 2015 and again mysteriously fell gravely ill in 2017. The Kremlin denied any involvement in Kara-Murza’s illness.
This story has been updated to correct the spelling of Navalny’s spokesperson.