Alexei Navalny, a prominent critic of Russian President Vladimir Putin, says he began a hunger strike in prison on Wednesday.
The Russian opposition leader was transferred to a prison outside Moscow in February in connection with an embezzlement case seven years ago. He nearly lost his life in a suspected poisoning with a nerve agent last year.
A post on Navalny's Twitter account on Thursday said that his weight had fallen to 85 kilograms from 93 kilograms since he has been in prison. He says he is being tortured with sleep deprivation as he is woken up eight times every night. Navalny has also complained of strong pains in his back and legs.
Russia's presidential spokesperson Dmitry Peskov said on Thursday that this is not an issue for the head of state.