Russian prosecutors said on Thursday they saw no need for a criminal investigation into the sudden illness of Kremlin critic Alexei Navalny, who his supporters suspect was poisoned, as they had found no sign that any crime had been committed.

The Interior Ministry said it had started a preliminary investigation into the case, but this was routine.

Navalny, 44, was airlifted to Germany on Saturday after collapsing during a flight from the Siberian city of Tomsk to Moscow. He is in a medically-induced coma in a Berlin hospital and his supporters said on Thursday his condition remained serious, with no major reason for optimism.

The hospital said its initial medical examination pointed to poisoning, though Russian doctors who had treated Navalny in a Siberian hospital have contradicted that diagnosis.

The Kremlin has so far defied calls from Germany, the United States and other powers to investigate the circumstances around Navalny’s illness, saying there is no reason to do so until poisoning is definitively confirmed.

While a statement by the Russian Prosecutor General’s office said it did not see the need for an investigation, it said German authorities have agreed to cooperate with Russia on the case. The office said it had asked Germany to share information about Navalny’s treatment and promised to give some back in exchange.

The Siberian branch of the Interior Ministry’s transportation unit said it was carrying out a preliminary investigation after Navalny’s flight made an emergency landing in the city of Omsk.

It had inspected the hotel room where Navalny had stayed in Tomsk and the routes he had taken in the city, as well as analysing video surveillance footage from the area, it said. The ministry did not find any drugs or other potent substances.

Navalny’s supporters have repeatedly said they believe Navalny was poisoned, pointing to his symptoms as well as the German clinic’s initial diagnosis.

“What more does the Prosecutor’s Office need … for them to have a reason to open an investigation?” asked Lyubov Sobol, a close Navalny ally.

Navalny has long been a thorn in the Kremlin’s side, exposing what he says is high-level graft and mobilising crowds of young protesters. He has been repeatedly detained, sued over his investigations into corruption and barred from running in the 2018 presidential election.

“I want to say straight off, there should be no super optimistic expectations right now … The assassination attempt was very serious, it was almost successful,” Leonid Volkov, the chief of staff for Navalny’s campaign, said in a live YouTube briefing.

“It was very lucky, his system was strong and it didn’t kill him … We must understand that we will not get our Alexei back soon the way that he was,” Volkov added.

The Kremlin has dismissed as “hot air” allegations by Navalny’s supporters that it was somehow involved in his illness.

European Union ministers are set to discuss Navalny’s condition this week.

Russia is already under Western sanctions after its annexation of Crimea from Ukraine six years ago, and another stand-off with European nations or the United States may hurt its economy further.

Reuters