Alexei Navalny is among Russian President Vladimir Putin's fiercest critics. (File)
Russian medics have agreed to allow the medical evacuation of the opposition leader Alexei Navalny from a Siberian hospital at his relatives' request, the hospital's deputy chief doctor said on Friday.
Navalny, a 44-year-old lawyer and anti-corruption campaigner who is among Russian President Vladimir Putin's fiercest critics, is in a coma in intensive care in the Siberian city of Omsk and his relatives have a plane waiting to evacuate him to a hospital in Germany.
"We... took the decision that we do not oppose his transfer to another hospital, the one that his relatives indicate to us," the deputy chief doctor at the Omsk hospital, Anatoly Kalinichenko, told journalists.
He said Navalny's condition had "stabilised" and his wife and brother "took the risks on themselves" for moving him.
The permission came after Navalny's family ramped up pressure on the authorities to agree a transfer, while medics had insisted Navalny's condition was too "unstable" for him to be moved.
Navalny's wife Yulia appealed directly to Putin to permit her husband's evacuation and her aides also asked the European Court of Human Rights to intervene with the Russian government.
German doctors who flew in on the air ambulance visited Navalny earlier Friday and the NGO that chartered the plane, the Cinema for Peace foundation said they were "able and willing" to fly him to Berlin.
The Kremlin critic fell ill on a plane from the city of Tomsk to Moscow on Thursday and it had to make an emergency landing in Omsk.
His aides say he was poisoned, apparently after drinking tea in the cafe of the Tomsk airport, while Russian doctors said they did not find any traces of poison.
"The diagnosis of poisoning was finally ruled out," Kalinichenko said.
Russian doctors said their preliminary diagnosis was a "metabolic disorder" caused by a sudden drop in blood sugar levels.
Kalinichenko said the Russians had a consultation with the German doctors and they examined Navalny.
"They were fully satisfied with all they saw, they agreed with our diagnosis," he said.
"The brigade (of German doctors) considered the patient transportable," he said. "They guaranteed they would get him to the destination, Berlin as we understand."
He said Russian doctors nevertheless initially thought that a transfer was "premature."
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