Russian opposition politician Alexei Navalny has been poisoned and is in intensive care, his spokeswoman said.
Mr Navalny felt unwell on a flight back to Moscow from Tomsk, a city in Siberia, according to Kira Yarmysh.
She tweeted: “The plane made an emergency landing in Omsk. Alexei has a toxic poisoning.”
Mr Navalny is unconscious and was placed on a ventilator in an intensive care unit.
According to Ms Yarmysh, he must have consumed something from the tea he drank this morning.
“Doctors are saying the toxin was absorbed quicker with hot liquid,” she said, adding that Mr Navalny’s team called police to the hospital.