Russian President Vladimir Putin critic Alexei Navalny, who has been on a hunger strike in prison for more than a week, says his guards taunt him by frying chicken in front of him.

"I go to the kitchen for a drink and a prison guard is standing there frying chicken," Newsweek quoted Navalny as saying on an Instagram post. "All the rules and regulations have been canceled," he said.

Navalny went on a hunger strike to protest "miserable medical care" at a Russian prison. The opponent of Putin, Navalny, 44, was sentenced in February for violating his parole. Navalny said he couldn't comply with the parole terms because he had been poisoned with a nerve agent.

Russian authorities detained the leader of the Navalny-backed Alliance of Doctors union after members tried to get into the prison to talk to his doctors.

According to his lawyers, Navalny has been diagnosed with two spinal hernias and his health has deteriorated, BBC reported.

Agnes Callamard, Amnesty International secretary-general, said Russian authorities are killing Navalny by "slow death" and seeking to hide what is happening to him," Reuters reported.

His conditions in prison amount to "torture," Callamard said.

U.S. President Joe Biden is "disturbed" by Navalny's poor health condition, White House press secretary Jen Psaki said.

Navalny wrote that he was undertaking a "100% hardcore prison hunger strike. Without any tricks like sweet tea, salted water, juice, vitamins etc. Only water," Newsweek reported.