MOSCOW (Reuters) — Jailed Kremlin critic Alexei Navalny declared a hunger strike on Wednesday in an attempt to force the prison holding him outside Moscow to provide him with proper medical care for what he said was acute pain in his back and both legs.

The fate of Navalny, one of President Vladimir Putin’s most prominent critics, is in focus after he said last week that being woken up by a guard every hour during the night amounted to torture and that his appeals for treatment for acute back and leg pain had been ignored.

In a handwritten letter addressed to the governor of his prison which was posted to social media by his team on Wednesday, Navalny said his daily requests for a doctor of his choice to examine him and for proper medicine for his problems to be provided had been ignored.

“I demand that a doctor be allowed to see me, and until this happens, I am declaring a hunger strike,” he said in the letter.

The IK-2 corrective penal colony 100 km east of Moscow did not immediately respond to a request for comment. Prison authorities, after examining Navalny last week, declared his condition to be stable and satisfactory. The Kremlin has declined to comment on his health.

Medical professionals on Sunday published an open letter demanding the 44-year-old opposition politician get proper care.

“We fear for the worst. Leaving a patient in this condition … may lead to severe consequences, including an irreversible, full or partial loss of lower limb functions,” the letter said.

Navalny was jailed last month for two and a half years on charges he called politically motivated. He was arrested as he returned to Russia from Germany in January, where he had been recovering from what doctors said was a nerve agent poisoning.

The West, including the European Court of Human Rights, has demanded Russia release Navalny. Moscow has called such appeals unacceptable interference in its internal affairs.