At least 52 people have been killed in a prison riot in Brazil which saw rival gangs battle for five hours, officials say.
Gang members from one prison block invaded another part of Altamira jail in Pará state, local media reported.
Officials giving a news conference said 16 of the dead were decapitated. Other reports said part of the prison was set on fire, suffocating many.
Two prison officers who were taken hostage have since been freed.
The violence began at around 07:00 local time (10:00 GMT), and ended at around noon, officials said.
Video reported to be from the prison carried by Brazilian media showed smoke billowing from at least one prison building, while another clip appeared to show inmates walking around on the rooftops.
The two rival gangs involved have not been named by authorities.
Violence in Brazilian prisons is not uncommon. The country has the world's third-largest prison population of some 700,000 people, and overcrowding is a widespread problem.
Clashes between rival gangs are frequent, as are riots