Russian opposition leader Alexey Navalny was poisoned, German doctors from a clinic where he is being treated announced on Monday.

“The team of doctors thoroughly examined the patient after his arrival. The clinical findings indicate intoxication by a substance from the active substance group of Cholinesterase inhibitors,” Charite clinic said in a statement on its official website, adding that presence of cholinesterase “has been proven several times and in independent laboratories”.

Currently, Navalny is in an intensive care unit and remains in a medically induced coma. His condition is serious, but there is no acute danger to his life, it added.

“In accordance with the diagnosis the patient is treated with the antidote atropine. The outcome of the disease remains uncertain and late consequences, especially in the area of the nervous system, cannot be ruled out at this time,” it said.

The physicians are in close contact with Navalny’s wife and her permission was sought before making the statement, it said.

Navalny, 44, a vociferous critic of President Vladimir Putin, fell ill on a flight from the Siberian city of Tomsk to Moscow last week.

The plane made an emergency landing in the city of Omsk and Navalny was rushed to a hospital, where he spent two days before being shifted to Berlin.

Commenting on the incident, Kremlin spokesman Dmitry Peskov earlier said they were waiting for test results before launching an investigation.

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