Russian opposition figure Alexei Navalny is unconscious in hospital with suspected poisoning, his spokeswoman has said.
The anti-corruption campaigner fell ill during a flight and the plane made an emergency landing in Omsk, Kira Yarmysh said on Twitter.
She said they suspect that Mr Navalny was poisoned by something mixed into his tea.
Mr Navalny is a staunch critic of President Vladimir Putin.
In June he described a vote on constitutional reforms as a "coup" and a "violation of the constitution". The reforms allow Mr Putin to serve another two terms in office.
"This morning Navalny was returning to Moscow from Tomsk," Ms Yarmysh tweeted.
"During the flight, he felt ill. The plane made an urgent landing in Omsk. Alexei has toxic poisoning. Right now we are going to hospital.
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.
Ms Yarmysh later said Mr Navalny was in intensive care.
The claims have not yet been independently verified.
Mr Navalny made a name for himself by exposing rampant corruption, labelling Mr Putin's United Russia as "the party of crooks and thieves".
In 2011 he was arrested and imprisoned for 15 days following protests over vote-rigging by Mr Putin's United Russia party in parliamentary elections.
Mr Navalny was briefly jailed in July 2013 on embezzlement charges but the sentence was widely seen as political.
U.S. President Joe Biden proposed a summit meeting with Russian President Vladimir Putin during a telephone call on Tuesday in which he stressed the U.S. commitment to Ukraine's territorial integrity and voiced concern about a Russian military build-up in Crimea and on Ukraine's borders,...( ) Read all
The European Bank for Reconstruction and Development (EBRD) is enforcing rights under its financing and security documents with regards to Danube Logistics Holding BV’s shareholding in Danube Logistics SRL (Danube Logistics), the operator of Giurgiulesti International Free Port in the...( ) Read all
EBA Moldova is following with great concern the latest developments regarding Danube Logistics SRL, the owner and operator of Giurgiulesti International Free Port, the only port of the Republic of Moldova.( ) Read all
The European Bank for Reconstruction and Development (EBRD) intends to fight a legal decision to impose external administration over the assets of Danube Logistics SRL, the operator of Giurgiulesti International Free Port in Moldova.( ) Read all
One August day in the mid-1960s, my parents boarded a bus in the village of Hartopul Mare in the center of Moldova to travel to the capital Chisinau, determined to get a better education and better jobs in the Soviet planned economy. It was a 90-minute trip in a vehicle packed with about 50...( ) Read all
On Thursday 3 December, the Parliament of the Republic of Moldova voted on a number of legislative proposals, including on limitations of Presidential powers, tabled in a hasty and non-transparent manner.( ) Read all
Seven people died from methanol (wood alcohol) poisoning after drinking hand sanitizer at a party in Russia. Nine people, with ages ranging from 27 to 69 years old, were partying when they opted to drink hand sanitizer after running out of alcoholic beverages, according to local Russian...( ) Read all
On 25 August 2020 the Constitutional Court of the Republic of Belarus (thereinafter – the CCRB) adopted a document entitled the “Constitutional Legal Position on the Protection of the Constitutional Order” (Kонституционно-правовaя позиция по...( ) Read all
Leaked documents shed a light on Deutsche Bank's central role in facilitating financial transactions deemed suspicious. Many of these could have enabled the circumvention of sanctions on Iran and Russia.( ) Read all