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As prominent Kremlin critic Alexei Navalny fights for his life in hospital, authorities in Russia are contradicting themselves about whether the opposition leader has been poisoned.

On Friday morning, the head of Navalny’s Anti-Corruption Foundation Ivan Zhdanov told journalists that police reported that a “poison” was found in Navalny’s system and that it was “dangerous to those around him” — though law enforcement wouldn't name the substance.

But, an hour later, officials from the hospital in Siberia where Navalny is being treated contradicted that assertion, saying they have so far found “no trace” of poison in Navalny’s system during testing.

“Poisoning as a diagnosis remains on the back burner, but we don’t believe that the patient suffered from poisoning,” Anatoly Kalinichenko, Omsk hospital deputy chief doctor, told reporters Friday.

Later, Alexander Murakhovsky, the chief physician at Omsk hospital, said during a press conference that doctors had come up with “five provisional diagnoses,” but added, “Unfortunately, I can’t name them at this time.”

Authorities said Navalny’s family had been informed of the diagnoses, but Kira Yarmysh, the press secretary for the Anti-Corruption Foundation, tweeted that the family had only been told about his symptoms.

“What they were told is a set of symptoms that can be interpreted in different ways,” Yarmysh tweeted. “Doctors still cannot establish the cause of Alexey's condition.”

Navalny’s aides and his wife, Yulia, are now trying to take him from the regional hospital to a specialist poison center in Germany — but his doctors are blocking their efforts.

On Friday morning, an air ambulance departed Germany and landed in the airport in Omsk, ready to transport Navalny to the center.

Doctors said that while Navalny’s condition had improved overnight, he was still too unstable to be transported because of “metabolic disorders and a sharp drop in blood sugar levels.”

The Russian government, who many critics believe is behind the attack on Navalny, wished the Kremlin critic a speedy recovery, and on Friday morning Dmitry Peskov, a spokesperson for President Vladimir Putin, said that the German doctors who had flown to Omsk had been invited to speak to their Russian counterparts.

But Yulia Navalny said she believes the doctors are blocking the move because it would allow independent specialists to determine what substance was supposedly used to poison her husband.

READ: Putin’s most vocal critic Is in serious condition after his tea was allegedly poisoned

Navalny fell ill on Thursday an hour into a flight from the city of Tomsk to Moscow. His plane made an emergency landing in Omsk, and he was taken to the local hospital, where he remains in a coma.

Yarmysh claimed that a cup of tea Navalny drank at the airport in Tomsk had been poisoned.

“We suspect that Alexei was poisoned by something mixed into [his] tea,” Yarmysh tweeted on Thursday. “It was the only thing he drank since morning. Doctors are saying that the toxic agent absorbed faster through the hot liquid.”

Cover: In this file photo taken on Saturday, Feb. 29, 2020, Russian opposition activist Alexei Navalny takes part in a march in memory of opposition leader Boris Nemtsov in Moscow, Russia. (AP Photo/Pavel Golovkin, File)

This article originally appeared on VICE US.