At least 52 prisoners were killed by other inmates during clashes between orgsed crime groups at the Altamira prison in northeastern Brazil on Monday, authorities said.
The Washington Post quoting the prison officials confirmed that as many as 16 among the victims were decapitated while others were asphyxiated.
It took five hours for prison officials to quell the riot in the Para state jail.
The clash erupted on early Monday after members of one gang infiltrated another part of the jail. Video and pictures aired by local media showed flames shooting out of the prison.
Two prison officials were taken hostage but were reportedly freed unharmed. The gangs were of the feared Comando Vermelho -- the Red Command, whose base of power in Rio de Janeiro -- and Comando Classe A.
"The state government will identify the leaders of the two factions involved in the confrontation so that we can put them in federal prisons," Para governor Helder Barbalho was quoted as saying.
Monday's clash marked the second time when a similar prison riot in northwestern Brazil in late May led to the death of 55 people, both by strangling and stabbing, by Brazil's third-most-powerful gang, in front of visiting families.
In early 2017, more than 120 inmates died in prisons across several northern states when rival gangs clashed over control of drug-trafficking routes in the region. The violence lasted several weeks, spreading to various states.
Brazil's prison population has swelled from about 500,000 inmates a decade ago to an estimated 800,000 at present.
Deteriorating conditions inside the prisons are one major reason behind Brazil's years-long war on crime. Some prisons are so overcrowded that inmates sleep standing up, with hands tied to bars to keep them upright.
President Jair Bolsonaro, elected last year on promises to crack down on violent crime, has described plans to "stuff prison cells with criminals."
"I'd rather a prison cell full of criminals than a cemetery full of innocent people," he had said.
"We will build more if necessary," the President added.
( With inputs from ANI )