Alexei Navalny, the jailed Russian opposition leader and prominent critic of Vladimir Putin, says he has been moved to a tiny cramped cell and deprived of visits in a move designed to shut him up.
A strong opponent of Russia's war in Ukraine, the 46-year-old had already been placed in solitary confinement on November 1 but says he could only be held there for two weeks.
Navalny said close family members had been due to visit him, but days beforehand prison officials told him he was considered an "egregious offender" and would be transferred to a small cell, where long visits were not allowed.
"So I will not have any more visits ... oh well, I'll take it philosophically. They're doing it to shut me up," he said in a series of posts on his social media account on Thursday.
"So what's my first duty? That's right, to not be afraid and not shut up," added Navalny, saying the decision to slash visiting times reflected "the real indescribable bestiality, very characteristic of the Kremlin".
He ended the posts by urging people to campaign against the war and Putin.
Navalny is serving prison terms totalling 11 and a half years in a maximum security jail 250 kilometres east of Moscow. He was convicted on charges -- fraud, contempt of court and parole violations -- that he, his supporters and Western nations reject as politically motivated.
Last month he said authorities had opened a new criminal case against him for promoting terrorism and extremism, potentially more than doubling his sentence.
Alexei Navalny was arrested in January 2021 upon returning from Germany, where he had been recuperating from nerve-agent poisoning he blames on the Kremlin.
Prior to his latest prison sentence, he was the driving force behind an anti-corruption site that exposed alleged wrongdoing by high-ranking Russian officials.