Jailed Russian opposition leader Alexei Navalny says he has been transferred permanently to solitary confinement.
Mr Navalny said the move took place just days before a planned family visit, and was aimed at silencing him.
He was already facing 11 and a half years in prison on a range of charges, including for fraud, which he said are trumped-up.
The 46-year-old has long been the most prominent face of Russian opposition to President Vladimir Putin.
Mr Navalny was already being held in solitary confinement, also called a “punishment cell”, but he could only be held there for 15 days, according to a post of his Instagram account.
But in a series of tweets on Thursday, the high-profile Kremlin critic said he had been accused by prison officials of being an “egregious offender” and moved to a “cell-type room”. His visitation rights have also been curtailed.
He said his new confinement is “a regular cramped cell, like the punishment cell, except that you can have not one but two books and use the prison kiosk, albeit on a very limited budget.”
Family members, – including his mother, father and wife Yulia – were due to visit him four days after he was moved, Mr Navalny said. He accused the Kremlin of “bestiality” and manually controlling his “entire incarceration”.
“They’re doing it to shut me up. So what’s my first duty? That’s right, to not be afraid and not shut up,” he wrote.
Mr Navalny is being held in a penal colony more than 250km (150 miles) east of Moscow. He was arrested on his return to Russia from Germany, where he had been treated after being poisoning with a nerve agent.
He was initially jailed for two and a half years for breaking bail conditions while being treated in hospital, but was then given an extra nine years for fraud and contempt of court.
In May he lost an appeal against a nine-year prison term on fraud charges, during which he launched a blistering attack on Russia’s war in Ukraine. He said the rulings against him were no different from the lies used by “madman” President Vladimir Putin and state TV to justify the war.
“You will suffer a historic defeat in this stupid war that you started. It has no purpose or meaning. Why are we fighting a war?” he said.
Russia has repeatedly silenced criticism of its war in Ukraine, prosecuting those who have refused to use the term “special military operation” and blocking independent media outlets.