The rebellion began when two rival gangs started fighting in an apparent settling of accounts

Prison official

Heavily-armed riot police who regained control of Urso Branco prison found evidence of an orgy of killing, with mutilated bodies piled high in cells.

The authorities put the number of dead at 27, but the archbishop of Rondonia, Moacyr Grecchi, said 45 inmates had been killed.

Relatives of convicts have been seeking information from the prison authorities.

Local press reports said the murdered inmates had been stabbed, shot, hung or flung off the roof. The gangs are said to have been armed with guns and knives.

Rioting erupted after a failed escape attempt on Monday.

"Two rival gangs started fighting in an apparent settling of accounts," a prison official was quoted as saying.

Overcrowded jails

Conditions inside the prison have long been a cause of concern and local human rights groups say they have repeatedly warned the authorities.

Riots are common in Brazil's overcrowded prisons, where many prisoners, lacking proper legal advice, are kept in detention for months after the end of their sentences.

A revolt last year, orchestrated from the notorious Carandiru prison, spread to nearly 30 jails across Sao Paolo state and left 16 inmates dead.

Human rights groups say Brazil has one of the worst records in the region on torture and abuse of prisoners.