One of the jailed members of the Pussy Riot protest band has vanished from sight since she was moved to a new prison 10 days ago, reports from Russia say.
The husband of Nadezhda Tolokonnikova told a US news website he had not received any news about her and her current location was being kept secret.
She had been on hunger strike at a penal colony in Mordovia.
She and another band member were jailed over a protest in a Moscow cathedral.
They were sentenced to two years' imprisonment after performing a crude protest song in February 2012. A third band member was released on appeal.
Moved by train
Tolokonnikova has complained of abuses by the prison staff in Mordovia.
Her husband said he last knew her precise whereabouts on 21 October, when guards put her on a train en route to a different prison.
She was seen on 24 October by a fellow passenger as the train arrived in the city of Chelyabinsk, in the Ural mountains.
Her husband, Pyotr Verzilov, told the Buzzfeed website he believed the decision to move his wife came from the authorities in Moscow: "They want to cut her off from the outside world."
He said Ms Tolokonnikova was still weak after two hunger strikes, and accused the authorities of trying to punish her because of her protests.
Pussy Riot's 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.