Prosecutors began the investigation on 20 August, the press service said on Thursday.
"More than 20 different forensic investigations (forensic, biological, physicochemical) are being conducted. At the moment, no highly hazardous or narcotic substances have been found," the statement read.
On 20 August, Russian opposition figure Alexei Navalny fell gravely ill during a domestic Russian flight. Following an emergency landing in the Siberian city of Omsk, he was taken to a local hospital and, according to an open letter published by regional doctors on Wednesday, he arrived just 17 minutes after landing.
For the next 44 hours, doctors waged an uninterrupted struggle for his life, as he went into a coma and was put on an artificial lung ventilator.
Immediately after Navalny fell ill, his spokeswoman Kira Yarmysh rushed to claim that he might have been poisoned, alleging that a substance could have been mixed into his tea - the only thing he had that morning. However, shortly thereafter CCTV footage was shared online from the airport allegedly showing Navalny being handed a cup by his aide Ilya Pakhomov. It has therefore been suggested that whoever prepared the tea could not have known for whom it was eventually intended.
Upon conducting multiple tests involving experts from different fields, Russian doctors said that no traces of poison had been found, suggesting that Navalny's condition was caused by an abrupt drop of glucose in his blood due to a metabolic imbalance.
On 24 August, German doctors claimed they had found traces of a substance from a group of cholinesterase inhibitors in his body, which Russian doctors denied, citing the patient's test results.
On Wednesday, the Russian medics published an open letter decrying the criticism they have faced after Navalny's transportation to the German clinic, Charite, and called the situation around the activist a "political diagnosis."
