Jailed critic of the Russian government Alexei Navalny says he is going on a hunger strike.
The 44-year-old, who is Russian president Vladimir Putin’s most outspoken opponent, was arrested on January 17 upon his return from Germany.
He was returning from spending five months there recovering from a nerve-agent poisoning that he blames on the Kremlin.
Russian authorities reject the accusation.
Last month, Navalny was sentenced to two-and-a-half years in prison for violating the terms of his probation while convalescing in Germany.
Taking to Twitter on Wednesday, he said: "Every convict has the right to invite a specialist for examination and consultation.
"Even with me, even though I'm innocent.
"Therefore, I demand that a doctor be allowed to see me, and while this has not happened, I am going on a hunger strike."
Navalny claimed earlier this month his physical condition was worsening in prison and that prison authorities were refusing to allow his doctor to visit him.
In a letter he complained that hourly checks by a guard at night amounted to sleep deprivation torture.
Copies of his letters to penitentiary officials and Russia’s top prosecutor were posted on Navalny's website.
The sentence stems from a 2014 embezzlement conviction that Navalny has rejected as fabricated — and which the European Сourt of Human Rights has ruled to be unlawful.
“My condition has worsened. I feel acute pain in my right leg, and I feel numbness in its lower part,” Navalny wrote in one of the letters. “I have trouble walking.”