Supporters of prominent Vladimir Putin foe Alexei Navalny claimed the Kremlin is risking his life by refusing to allow him to be flown to Germany for treatment.
Mr Navalny, 44, is in grave condition in a "deep coma" after becoming suddenly sick on a plane from Tomsk to Moscow on Thursday.
He became unwell shortly after take-off and his aides and family believe his tea was spiked with poison at Tomsk airport before his flight.
The aircraft made an emergency landing in Omsk and he was rushed to hospital. Intensive care specialists, neurophysiologists and anaesthetists were sent from two top Moscow clinics, the Pirogov Medical and Surgical Centre and the Burdenko Centre of Neurosurgery to treat Putin's opposition leader.
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