Russia's prison service says it has moved one of the two imprisoned members of Pussy Riot, an all-female punk rock band, to a hospital.
Officials said Friday Nadezhda Tolokonnikova was taken to a hospital in Mordovia province.
Band mate Yekaterina Samutsevich said Tolokonnikova had complained about headaches.
Tolokonnikova, Samutsevich and Maria Alyokhina were sentenced last year to two years in prison for an anti-Vladimir Putin performance in a Moscow church. They were found guilty of hooliganism motivated by religious hatred.
Samutsevich was given a suspended sentence and freed on appeal.
Critics have accused President Putin of launching a mass crackdown on dissent since he took office in May. The Kremlin maintains that new laws have been passed to strengthen security and keep the public safe.