Russian doctors say leading opposition figure Alexei Navalny – who supporters believe was poisoned – 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.
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.
German doctors have now been given access to him in hospital, one of his aides told reporters.
At a news conference in Berlin, Leonid Volkov said a medically equipped plane sent from Germany was still waiting for him in the Siberian city of Omsk, where he is in hospital.
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.