Russian opposition figure Alexei Navalny has been deliberately hospitalized with suspected poisoning, his spokeswoman said.
The anti-corruption campaign fell ill during a flight and the plane made an emergency landing in Omsk, Kira Yarmysh said on Twitter.
She said she thought Mr Navalny was poisoned by something mixed into his tea. A hospital has confirmed his admission.
Mr Navalny, 44, is a staunch critic of President Vladimir Putin.
In June, he described a vote on constitutional reform as a “coup d’etat” and a “violation of the constitution”. The reform allows Mr Putin to serve two more terms in office.
- Russia’s worthy Putin critic
What did the spokeswoman say?
Kira Yarmysh, the press secretary for the anti-corruption foundation Mr Navalny founded in 2011, tweeted: “This morning Navalny was back from Tomsk to Moscow.
“During the flight he felt wrong. The plane made an urgent landing in Omsk. Alexei has toxic poisoning. At the moment we are going to the hospital.”
She added: “We think Alexei was poisoned by something that was mixed up [his] tee. It was the only thing he had been drinking since morning.
“Doctors say the toxic agent is rapidly absorbed by the hot liquid. At the moment, Alexei is conscious.”
Ms Yarmysh later tweeted that Mr Navalny was in intensive care, on a ventilator and still conscious, and that police were called.
The news agency Tass reported that the Omsk Emergency Hospital had confirmed his admission and that he was in a serious condition.
Images on social media showed Mr Navalny being taken on a stretcher to an ambulance at the airport.
Who’s Alexei Navalny?
He made a name for himself by exposing official corruption, by branding Mr Putin’s United Putin as “the party of villains and thieves”, and has served several prison terms.
In 2011, he was arrested for 15 days and imprisoned after protests over voting rights by the United Russia party in the parliamentary elections.
Mr. Navalny was briefly jailed in July 2013 on charges of sustainability, but condemned the sentence as political.
He tried to stand in the 2018 presidential race, but was expelled due to previous convictions of fraud in a case he again said was politically motivated.
Mr. Navalny also received a 30-day prison sentence in July 2019 after asking for unauthorized protests.
He was taken ill during that imprisonment. Doctors diagnosed him with “contact dermatitis”, but he said he had never had acute allergic reactions and his own doctor suggested he might have been exposed to “some toxic agent”. Mr Navalny also said he thought he may have been poisoned.
Mr. Navalny also suffered a serious chemical fire in his right eye in 2017, after being attacked with antiseptic dye.