Story updated on July 30, at 1:27 am.
At least 57 inmates were killed during a prison riot in northern Brazil on Monday.
The riot began early in the morning at the Altamira prison in northern Para state. State prison chief Jarbas Vasconcelos said in a statement that members of one gang, the Comando Classe A, set fire to a cell containing inmates of the rival Comando Vermelho gang. Video and pictures aired by local media showed flames shooting out of the prison.
Authorities say 16 of the dead inmates were decapitated. Two guards were taken hostage during the riot, but were eventually freed.
The incident was reminiscent of riots in May when 55 inmates were killed in gang-related violence at four prisons in the neighboring state of Amazonas.
Human rights groups have accused the government of Brazil of doing little to deal with the country's notoriously troubled and overcrowded prisons. The prison population swelled from about 500,000 inmates a decade ago to an estimated 841,000 last year.