BERLIN — Russia’s most prominent opposition figure, Aleksei A. Navalny, arrived in Berlin for treatment on Saturday, more than 48 hours after falling into a coma in Siberia in what his family and supporters suspect was a deliberate poisoning.
Mr. Navalny was admitted to Charité, one of Germany’s leading medical research facilities, where he will undergo “extensive diagnostic tests” the hospital said in a statement hours after the plane transporting him touched down.
“Patient stable, mission accomplished,” said Jaka Bizilj, who runs the foundation that had organized the air transport at the urging of Mr. Navalny’s friends and family.
Mr. Navalny, who remained in a coma after falling ill on a flight within Russia on Thursday, was in stable condition throughout his Saturday-morning journey from the Siberian city of Omsk to Berlin, said Mr. Bizilj, who founded and runs the Cinema for Peace foundation, which organized the air ambulance.
The arrival in Germany of Mr. Navalny, who is the most persistent critic of President Vladimir V. Putin of Russia, comes as Moscow is watching popular uprisings in Khabarovsk in its Far East, and in neighboring Belarus, where thousands have taken to the streets to protest an election on Aug. 9 whose results were widely seen as falsified.
Mr. Navalny, who had been in Siberia meeting with opposition candidates in an upcoming local election, had rejoiced at the recent unrest as an inspiring sign that even longstanding political systems can be changed.
Upon landing in Berlin after roughly seven hours in the air, Mr. Navalny’s plane was met by an ambulance that brought him, under police escort, to the hospital where he was admitted and will undergo an examination.
“After completion of the examinations and after consultation with the family, the attending doctors will comment on the illness and further treatment steps,” Manuela Zingl, a spokeswoman for Charité, said in a statement. “The examinations will take some time. We therefore ask for your patience; we will inform you as soon as we have any findings.”
Doctors at the hospital treated Pyotr Verzilov, a member of the Russian protest group Pussy Riot, in 2018, and found that he was likely to have been poisoned. Speaking to reporters via video link on Friday, Mr. Verzilov said the onset of his symptoms had mirrored those of Mr. Navalny, including a loss of consciousness and his slipping into a coma several hours after the suspected poisoning.
“The similarities are striking, not only in the medical condition, but in the behavior of Russian government and doctors,” Mr. Verzilov said, pointing out that his own transfer out of Russia was also delayed until more than two days after the suspected poisoning took place. Critics have said such delays on the part of Russian officials make it harder to determine what substance has been ingested.
Mr. Navalny had collapsed in agonizing pain on Thursday shortly after takeoff on what was to have been a 2,000-mile flight to Moscow. His family suspects that poison may have been added to a cup of tea he drank in the airport hours before boarding that flight.
His evacuation came only after hours of wrangling with Russian doctors and officials, who had insisted that a transfer to Germany would endanger Mr. Navalny’s health. But a team of German doctors, who had arrived in Omsk on the air ambulance, were granted access to the opposition leader Friday afternoon and they stated unequivocally that it was safe for him to travel and he was cleared to board the plane.
Mr. Navalny’s wife, Yulia, who had sent Mr. Putin a letter on Friday requesting permission to evacuate her husband, was allowed to accompany him to Germany.
The Russian authorities have consistently denied any evidence exists of poisoning. At a news conference on Friday, Dr. Aleksandr Murakhovsky said tests for toxins in Mr. Navalny’s blood were all negative. He said Mr. Navalny had suffered an “imbalance in carbohydrates, that is, metabolic disorder,” possibly caused by low blood sugar.
Mr. Navalny’s wife and personal doctor quickly dismissed this account, saying the idea that an otherwise healthy 44-year-old had suffered from low blood sugar was ridiculous.
If Mr. Navalny is found to have ingested dangerous toxins, he would become the latest prominent Kremlin critic in recent years to have been the victim of a poisoning.
A fatal dose of the radioactive substance polonium 210 was used against Alexander Litvinenko and a nerve agent called Novichok against Sergei Skripal, both former Russian intelligence officers attacked in England. The former Ukrainian President Viktor Yushchenko fell ill from a dioxin, and unknown toxins were used against Vladimir Kara-Murza, a Russian journalist who lobbied in the West for sanctions against Kremlin operatives.
In all these cases, the person or persons who ordered the attacks has remained unknown and, despite attempts to take cases to higher courts, including the European Court of Human Rights, justice has not been served.
Officials in Berlin did not immediately comment on Mr. Navalny’s arrival, fully aware of the sensitivity of the issue. But in offering earlier this week to allow the opposition leader into Germany for medical treatment, Chancellor Angela Merkel called for a through investigation into what had happened.
“What is particularly important is that the circumstances behind this are cleared up very quickly,” she said. “We insist on this, because what we have heard so far is very unfavorable. It must be done very transparently.”