Jailed Kremlin critic Alexei Navalny went on hunger strike on Wednesday in an attempt to force the jail holding him outside Moscow to provide him with proper medical care for what he said was acute pain in his legs and back.

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

In a handwritten letter addressed to the governor of his jail which was disseminated on social media by his team on Wednesday, Navalny said daily requests for a doctor of his choice to examine him and for proper medicine had been disregarded.

“I really need a doctor. Every convict has the right (by law) to invite a specialist to examine and consult him. Even I have such a right and I’m innocent,” Navalny wrote in the letter.

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

After examining Navalny last week, prison authorities declared his condition to be stable and satisfactory. The Kremlin has declined to comment on his health, noting that it is a matter for the federal penitentiary service.

On Wednesday, the penitentiary service said Navalny was receiving all necessary treatment.

“The convict A. Navalny is provided with all the necessary medical aid in accordance with his current medical conditions,” Interfax news agency cited the federal penitentiary service of the Vladimir region as saying in a statement.

It added that regular checks of prisoners during the night were carried out in line with the law and “do not hinder the rest of the convicts”.