MOSCOW — Aleksei A. Navalny, the imprisoned Russian opposition leader, declared a starvation strike on Wednesday in protest over what he mentioned was jail officers’ failure to supply him with correct medical take care of extreme ache in his again and his proper leg.

In a handwritten letter to the jail warden, Mr. Navalny, essentially the most vocal critic of President Vladimir V. Putin, complained that regardless of his worsening situation, he has not been allowed to see a physician of his alternative or obtain essential medicine.

Mr. Navalny, who suffered a near-fatal poisoning in August, wrote within the letter, posted on-line by his supporters, that he wanted “to see a physician very badly” and that he wouldn’t finish his starvation strike “earlier than it occurs.” The jail employees, he added, had additionally ordered a marketing campaign of psychological harassment in opposition to him, together with sleep deprivation.

Mr. Navalny had mentioned in an earlier assertion that jail medical doctors had offered solely ibuprofen capsules to deal with the ache, describing the jail as “an actual focus camp 60 miles away from Moscow.”

The jail service said in a statement on Wednesday that Mr. Navalny has obtained the entire medical assist he wants and that guards have been required to verify that inmates have been current of their beds.

Mr. Navalny collapsed into a coma on an airplane flight final August and was medically evacuated from Russia to Berlin.

After intensive assessments there, each the German and French governments, and worldwide chemical weapons specialists, confirmed that he had been poisoned with a Soviet-designed army nerve agent, Novichok. Mr. Navalny said the attempt on his life was ordered by the Kremlin.

Mr. Putin has denied any state position within the poisoning, arguing that if the Russian state had needed to kill him, it will have succeeded.

On Tuesday, Mr. Putin mentioned Mr. Navalny’s scenario with Chancellor Angela Merkel of Germany and President Emmanuel Macron of France, who demanded that his rights be revered. European Union officers have known as for Mr. Navalny’s instant launch.

Mr. Navalny’s means to succeed in thousands and thousands of his followers by way of social media with the assistance of his legal professionals and others signaled that he may stay a menace to Mr. Putin’s grip over Russia, even whereas in jail. After a sequence of large-scale protest demonstrations demanding his launch in January, his group introduced extra protests this spring.