About fifty-seven people have died in a jail 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.
Sixteen of the dead were decapitated and the remainder suffocated after part of the prison was set on fire.
Two prison officers who were taken hostage have since been freed.
The violence began at about 07:00 local time (10:00 GMT) on Monday, and ended at around noon, officials said.
Members of the Comando Classe A (CCA) gang set fire to a cell where rival gang members from Comando Vermelho (Red Command) were kept, the Pará state government said in a statement.
The structure of the cell allowed the fire to spread quickly, resulting in the death by suffocation of some inmates.
The government statement said there had been no prior warning or signs of an impending attack on this scale.