Russian doctors treating opposition leader Alexei Navalny remains too ill to be moved to Germany for treatment.
Mr Navalny has been in a coma since Thursday when he fell ill on a flight. His supporters called the doctors’ decision “a direct threat to his life”.
The doctors say no poison was found in his body. However, his supporters believe he was poisoned.
The prominent critic of President Vladimir Putin has consistently exposed official corruption in Russia.
He has served multiple jail terms.
His team suspects a poisonous substance was put in his tea at an airport cafe in the city of Tomsk as he prepared to fly to Moscow.
Berlin-based Cinema for Peace Foundation organised an air ambulance to pick up Mr Navalny from the Siberian city of Omsk and bring him back to Berlin, Germany.
In a preliminary diagnosis on Friday, doctors said his condition might be the result of a “metabolic disorder” caused by low blood sugar.
The head doctor at the hospital treating Mr Navalny in Omsk in Siberia said the patient was too unstable to be transferred and that legal questions would need to be resolved before any move.
Mr Navalny’s team said it was “deadly” for him to remain in the hospital.
“The ban on the transportation of Navalny is an attempt on his life,” his spokeswoman Kira Yarmysh wrote on Twitter.