Navalny, 44, fell ill last Thursday on a flight back to Moscow from Tomsk, a city in Siberia, and was airlifted to Berlin last weekend.
Charite hospital in Berlin said this week that its initial medical examination pointed to poisoning, though Russian doctors who treated Navalny in Siberia have contradicted that diagnosis.
Navalny remains in intensive care and on a ventilator, but some of his symptoms have improved, Charite hospital said in a statement on Friday.
“While his condition remains serious, there is no immediate danger to his life. However, due to the severity of the patient’s poisoning, it remains too early to gauge potential long-term effects,” the hospital said.
Navalny, a fierce critic of Russian President Vladimir Putin, fell ill on the flight last Thursday after drinking a cup of tea laced with poison, his supporters said, without producing evidence. The plane was forced to make an emergency landing.
After he was airlifted to Germany, doctors there said they found indications of cholinesterase inhibitors in his system. Cholinesterase inhibitors, which are found in some pesticides and chemical nerve agents, block the breakdown of a key chemical in the body, acetylcholine, which transmits signals between nerve cells.
On Friday, German Chancellor Angela Merkel told reporters at her annual summer news conference that it was “right and good” that Germany had aided Navalny. “And now we will try to get this cleared up with the possibilities we have,” she added.
Germany will try to ensure a “European reaction” to the incident once there is more clarity about what happened, Merkel said.
She cited the poisoning of former Russian spy Sergei Skripal and his daughter in Britain two years ago, which prompted many European countries to expel Russian diplomats.
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Russian prosecutors said on Thursday they saw no need for a criminal investigation into the sudden illness of Navalny. But the office said it had asked Germany to share information about his treatment.
The Russian Interior Ministry also said it had started a preliminary investigation into the case, but added that this was routine.
Navalny has long been a thorn in the Kremlin’s side, exposing what he says is high-level graft and mobilizing crowds of young protesters. He has been detained repeatedly, sued over his investigations of corruption and barred from running in the 2018 presidential election.
The Kremlin has dismissed as “hot air” allegations by Navalny’s supporters that it was somehow involved in his illness.
Reuters and The Associated Press contributed.