Later, Deputy chief doctor of the Omsk hospital Anatoly Kalinichenko said his condition had stabilised and he could be moved if his family wished. Those responsible must be held to account. Ivan Zhdanov, director of Mr Navalny's anti-corruption foundation, said a police official had told him they had found a "deadly substance" that presented "a risk to the life of not just Alexei but those around him too".
The specific substance involved in the Navalny poisoning "remains unknown", the hospital said.
"His health is serious but there is now no acute danger to his life", said the hospital, which the 44-year-old was admitted to on Saturday after an intervention by Chancellor Angela Merkel. "There are also direct effects of cholinesterase inhibitors on the brain", he said.
Nerve agents attack the enzyme that controls acetylcholine, leading to an overproduction and muscle malfunction.
However, hospital authorities denied poisoning saying that would have been much easier to diagnose if that were the case.
"Alexei Navalny's prognosis remains unclear; the possibility of long-term effects, particularly those affecting the nervous system, can not be excluded", the clinic stressed in the statement.
His wife, Yulia, sent Putin a letter Friday requesting permission to evacuate her husband for treatment.
Navalny is believed to have ingested the poison from a cup of black tea he had in the Tomsk airport, while flying back to Moscow.
"We are dealing with a patient who, it is fairly likely, was poisoned", Seibert told reporters in Berlin.
Navalny's team complained authorities wanted to stall for time so that any trace of what poisoned him would disappear.
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They said this case shows that while coronavirus patients develop antibodies, their levels could decrease after a few months. Chuang believes the upcoming massive screening will help identify unknown sources and cut transmission chains of the virus.
If Navalny is found to have been poisoned "that would represent a crucial moment in Russian Federation", he said.
Initial results are expected on Monday, with results from tests for radioactive material due later in the week, the paper said.
Navalny became ill on the morning of August 20 during a flight from Tomsk to Moscow, the plane urgently landed in Omsk, from where the oppositionist was taken by ambulance to the toxic resuscitation department.
He collapsed on a plane on Thursday last week after drinking tea that his allies said they believe was laced with poison.
"It is Putin who benefits from these endless assaults", Yashin said. The Kremlin hasn't yet commented on the allegation.
Doctors treating him in Omsk initially refused to let Navalny leave but had a change of heart after his family and staff demanded he be allowed to travel to Germany.
He said doctors had found nothing to support the idea that Navalny had been poisoned. If the plane's ascent had caused the coma, then another flight so soon might "threaten the life of the patient", he said.
When questioned about why law enforcement officers were present at the Omsk hospital, Murakhovsky said he could not say who it was and could not "say they were doing something".
Navalny was permitted by Russian authorities to leave the hospital in Omsk, Siberia, after his family, activists and worldwide leaders appealed directly to President Vladimir Putin. He had also endured chemical burns to his eye in 2017 when attackers threw a green antiseptic at his face outside his office.
Last year, Navalny was rushed to hospital from jail where he was serving a sentence on charges of violating protest regulations.