Pussy Riot's Nadezhda Tolokonnikova in prison clinic
Russian prison officials have moved a member of the punk band Pussy Riot to a medical unit at the penal colony where she is on hunger strike.
The news about Nadezhda Tolokonnikova was reported on Twitter by her husband, Pyotr Verzilov.
"Nadya is now in hospital, but they're refusing to provide documents about that, or to meet the defence [team]. A blockade has begun," he said.
Tolokonnikova has complained of abuses by the prison staff in Mordovia.
Her lawyer Dmitry Dinze, quoted by Russian media, said she was very weak, with low blood pressure and low blood sugar. She began a hunger strike on Monday.
Mr Dinze was also quoted as saying the administrators of penal labour colony No 14, where she is serving a two-year sentence, had been summoned to Moscow. It is not yet clear what the Moscow consultation is about.
After she went on hunger strike, Tolokonnikova was moved to an isolation cell for her own safety, the prison authorities said.
She and another band member, Maria Alyokhina, were jailed after performing a crude protest song in a Moscow cathedral. A third band member was released on appeal.
Their act was regarded as blasphemous by many Russians, but their prosecution caused an international outcry.
Mordovia, some 445km (275 miles) east of Moscow, has labour camps dating back to the notorious Gulag system set up by Soviet dictator Joseph Stalin.
Requests by Tolokonnikova and Alyokhina for parole were rejected. Tolokonnikova's release date is expected to be 3 March 2014.
On Thursday Tolokonnikova alleged that she had been left without drinking water in her cell and that a guard had grabbed her arms and shoulders. She described it as the first use of physical force against her, and urged the authorities to transfer her to a different prison.
The prison service denied her account, saying her water bottles had been replaced with warm water on doctors' advice and physical force had not been used against her.
In a letter released to media this week, Tolokonnikova said she had complained that she faced threats from other inmates, and also about long hours of forced labour.
She said female inmates were treated like "slaves", working 17 hours a day sewing police uniforms.
If they failed to meet their quotas they were punished by being denied food, prevented from using the bathroom or made to stand outside in the cold, she wrote.
The prison service denied those allegations, saying women worked no more than eight hours a day.