Russian prison officials said Monday that dissident Alexei Navalny has been moved to a prison hospital to receive “vitamin therapy” for his ailing health. Navalny’s physician, Yaroslav Ashikhmin, said his patient could “die at any moment.”

Navalny, 44, was arrested in January upon returning to Moscow from Germany, where he was treated for chemical weapons poisoning. Navalny accused Russian President Vladimir Putin of ordering FSB security agents to murder him.

Navalny’s arrest, ostensibly on charges of violating parole from an embezzlement conviction by visiting Germany for medical treatment, was denounced by the United States and most other Western governments.

Navalny announced a hunger strike on April 1 to protest his imprisonment and the lack of medical care he received for his already deteriorating health. He said his jailers responded by attempting to force-feed him.

On Sunday, Navalny’s doctors said they were denied access to their patient after waiting two hours outside the notorious Pokrov prison camp. Physician Yaroslav Ashikhmin and Russian Alliance of Doctors leader Anastasiya Vasilyeva denounced Navalny’s treatment and said his health is in serious jeopardy, as reported by Sky News:

Mr. Ashikhmin said Navalny could be on the verge of death, as latest test results show extremely high potassium levels, which put him at risk of cardiac arrest.

The physician also says he has high creatinine levels, which suggest his kidneys are damaged.

“Our patient could die at any moment,” he wrote on Facebook.

Ms. Vasilyeva called his treatment in jail ”cruel and monstrous” and she demanded “action must be taken immediately” to address his condition.

Several doctors wrote a letter to the regional branch of the Russian Federal Penitentiary Service (FISN) over the weekend, pleading for permission to examine him. According to Navalny’s lawyer, Olga Mikhailova, about 2,000 doctors have signed an open letter demanding doctors he trusts be granted access to him, possibly including the doctors who treated him in Germany. The Kremlin rebuffed these requests as unacceptable demands for “special treatment” of a prisoner.

Prison officials said Monday that Navalny has been transferred to a “regional hospital for convicts,” located in a different prison camp, but insisted his condition is not serious.

“Navalny’s health condition is assessed as satisfactory and he is examined daily by a general practitioner. The patient has been prescribed vitamin therapy with his consent,” the regional prison service stated.

The head of Navalny’s Anti-Corruption Foundation, Ivan Zhdanov, dismissed the prison statement as proof “Navalny’s condition has gotten so bad that even a torture farm acknowledges it.”

“It is absolutely clear that we will now be given something like ‘good news’ about Alexei’s condition before the rally. Don’t get fooled. We can only get truthful information from his lawyers,” Zhdanov said, referring to the massive protests planned to coincide with Putin’s state-of-Russia address on Wednesday evening.