BERLIN — A plane carrying a prominent Russian opposition figure to a German hospital for treatment of suspected poisoning took off early Saturday from a Siberian city, his spokeswoman said, after a day of delays in which Russian doctors offered a variety of reasons to block his transfer.
The opposition leader, Aleksei A. Navalny, who had been in a coma since Thursday, was being flown on a Challenger 604 air ambulance arranged by the foundation of a Berlin-based movie producer. The evacuation came after a team of German doctors who had arrived on the air ambulance stated unequivocally on Friday that it was safe for him to travel.
Mr. Navalny’s personal doctor, Anastasia Vasilyeva, said in an interview Friday that she believed the Russian authorities had tried to delay his departure long enough for the poison in his system to diminish and become difficult or impossible to identify.
The standoff had dragged on throughout the day Friday, with the evacuation plane idling at the airport.
Mr. Navalny fell suddenly and violently ill on Thursday on a flight to Moscow from the Siberian city of Tomsk, where he had met with local opposition candidates. The plane was forced to make an emergency landing in the nearby city of Omsk.
After Mr. Navalny’s arrival at the hospital in Omsk, his family and associates were bitterly critical of the authorities, who refused to release detailed information on his condition, denied he had been poisoned and contended that he was too unstable medically for travel.
The daylong refusal to allow Mr. Navalny’s transfer was effectively “an attempt on his life” being carried out by “doctors and the deceitful authorities that have authorized it,” Mr. Navalny’s spokeswoman, Kira Yarmysh, said.
Early Saturday, after the evacuation flight took off, Ms. Yarmysh tweeted: “The struggle for Alexei’s life and health is just beginning, and there is still a lot to go through, but now at least the first step has been taken.”
Upon arrival in Germany, Mr. Navalny was expected to be treated at a leading research hospital in Berlin, Charité.
“We were working like crazy through every possible channel to make this happen,” said Jaka Bizilj, the producer whose foundation sent the evacuation plane. “But I think the breakthrough was the report from the German medical team.”
Mr. Bizilj, who had previously arranged the transfer of a member of the Russian protest group Pussy Riot, who was likely poisoned, stressed that the German doctors were not toxicologists and did not give any assessment of what had caused Mr. Navalny’s illness.
Mr. Navalny, who is the most persistent critic of President Vladimir V. Putin of Russia, had collapsed in agonizing pain shortly after takeoff on what was to have been a 2,000-mile flight to Moscow. He drank a cup of tea in an airport cafe before departure.
His wife, Yulia, sent Mr. Putin a letter Friday requesting permission to evacuate her husband for treatment. The Kremlin had earlier said it was open to allowing Mr. Navalny to be flown abroad. But after the German hospital airplane arrived Friday morning, delays ensued.
The head doctor at Hospital No. 1 in Omsk, where Mr. Navalny was being treated, told journalists that he could not release his patient even if relatives requested he do so, because Mr. Navalny’s medical condition was too unstable.
Dr. Aleksandr Murakhovsky, who had a portrait of Mr. Putin in his office and is reportedly a member of the ruling party, United Russia, also offered the first diagnosis of what had befallen Mr. Navalny on the flight.
Mr. Navalny, he said, had suffered an “imbalance in carbohydrates, that is, metabolic disorder,” possibly caused by low blood sugar. He said doctors had found nothing to support the idea that Mr. Navalny had been poisoned.
His contention that Mr. Navalny, an otherwise healthy 44-year-old, had suffered from low blood sugar was quickly dismissed as ridiculous by the opposition leader’s physician, Dr. Vasilyeva.
“This is not a diagnosis,” she said. “If it were just a metabolic disorder he would not be in a coma or on ventilation.” Low blood sugar can be corrected quickly with an injection, she said.
The Kremlin spokesman, Dmitri S. Peskov, then offered another reason for delaying Mr. Navalny’s departure, noting that he had first become ill while on an ascending airplane. If the plane’s ascent had caused the coma, then another flight so soon might “threaten the life of the patient,” he said.
Dr. Vasilyeva rejected Mr. Peskov’s theory as “complete nonsense.”
In the interview, Dr. Vasilyeva described a curious encounter earlier reported by Mr. Navalny’s wife, Yulia, and members of his political movement but denied by the Russian authorities, pointing to another possible stalling tactic.
Dr. Vasilyeva said that she, Yulia Navalnaya and the chief doctor at the Siberian hospital, Dr. Murakhovsky, were discussing treatment when an official with Russia’s transport police entered the room and said Mr. Navalny had been poisoned with a substance so lethal it could endanger “those near him.”
Dr. Vasilyeva said the policewoman, who did not introduce herself, had said the substance was “very dangerous” and showed Dr. Murakhovsky the name of the toxin, written on a phone screen. The policewoman said she could not reveal it to others because it was “an investigative secret.”
Though the Russian security services are suspected of having used a range of exotic poisons to eliminate opponents, including radioactive polonium 210 and a military nerve agent, Mr. Navalny’s supporters suggested that the transport police, who monitor air safety, had raised the prospect to delay the evacuation.
“They are just artificially delaying so no toxic substance will be found in his blood,” Dr. Vasilyeva said.
The Russian authorities have consistently denied any evidence of poisoning. Dr. Murakhovsky, at a news conference Friday, denied this account of the meeting as conveyed by Mr. Navalny’s wife and personal doctor. He said tests for toxins in Mr. Navalny’s blood were all negative.
Melissa Eddy reported from Berlin and Andrew E. Kramer from Moscow. Mike Ives contributed reporting from Hong Kong.