At least 57 inmates were killed in a prison riot in Altamira jail in northern Brazil on Monday, AP reported. Sixteen of these inmates were decapitated, police officers said.

Para state prison authorities said a fight erupted around 7 am local time (3.30 pm Indian Standard Time) between the Rio de Janeiro-based Comando Vermelho and a local criminal group known as Comando Classe A. “Leaders of the (Comando Classe A) set fire to a cell belonging to one of the prison’s pavilions, where members of the (Comando Vermelho) were located,” a statement issued by the authorities said.

State prisons chief Jarbas Vasconcelos said the fire spread rapidly as the prisoners were held in old container units while the prison was being renovated. The blaze prevented police and rescue officials from entering the area for a long time, he added.

“It was a targeted attack,” Vasconcelos said. “The aim was to show that it was a settling of accounts between the two groups, not a protest or rebellion against the prison system.” No firearms were found during a search operation, only makeshift knives.

Jail authorities said 46 prisoners will be transferred to other facilities, 10 of whom will be imprisoned under stricter facilities. The Altamira prison has a capacity of 200, but currently holds 309 prisoners, BBC reported.

Prison riots in Brazil are not uncommon. At least 15 people were killed in a clash that broke out at a prison in Amazonas in May. The violence followed a riot in 2017 at the same prison when 56 inmates were killed in a clash. The country has the world’s third-largest prison population – 7,12,305 inmates till April this year.