One of the jailed members of the Pussy Riot rock group, Nadezhda Tolokonnikova, has been taken to hospital for tests, a spokeswoman for the Russian prisons service said on Friday.
Tolokonnikova "was transferred to hospital for a diagnostic examination based on her own and her lawyer's wishes," the spokeswoman told AFP without giving further details.
The activist is serving a two-year sentence at a prison camp in the Mordovia region in central Russia for staging an anti-Vladimir Putin performance last year in a Moscow church.
One other Pussy Riot member, Maria Alyokhina, is serving her two-year term in the Perm region. The third jailed band member Yekaterina Samutsevich was freed on appeal.
The spokeswoman for the Federal Service for the Execution of Punishment (FSIN) denied that Tolokonnikova was ill but could not reveal a diagnosis on grounds of medical secrecy.
Samutsevich had raised the alarm about Tolokonnikova's health in a late night interview Thursday with opposition Dozhd (Rain) television, revealing that she had been hospitalised and had been unwell for some time.
The hospitalisation was "not long ago. She has complained about her health for a long time," Samutsevich said.
"A decision was taken to take her to a neighbouring prison colony where there is a hospital. She has been there several days," she added.
She described the prison camp where Tolokonnikova is being held -- prison camp number 14 in the Mordovia region -- as notorious for its conditions and speculated this may have had an effect on her colleague.
"Every day she gets up at five and goes to work. She has two shifts. The problem is that they do not let her rest after that and give her other tasks," said Samutsevich.
"It means she is working all the time and is complaining of being very tired."
An attractive doe-eyed brunette, Tolokonnikova is the most recognisable member of the rock group and had a record of activism in the Voina (War) art group even before Pussy Riot was formed.
The concerns about Tolokonnikova's health flared on the same day a court in the Perm region was to hear a complaint by Alyokhina against several formal reprimands she has received over her behaviour in prison.
Pussy Riot's performance in the Christ the Saviour Cathedral outraged the church and shocked many in Russia. But their imprisonment divided society and for the opposition became one of the symbols of repression under Putin.
