At least 42 inmates were killed in clashes in seperate prisons in northern Brazil on Monday, authorities said, a day after violence in another jail left more than a dozen people dead.
At least 27 of the victims were in the Antonio Trindade Penal Institute near Manaus, the capital of Amazonas state, where the prisons are located.
The Amazonas state prison agency said the prisoners found dead on Monday all showed signs of asphyxia.
The federal government said it was sending reinforcements to boost security in the state’s prisons.
Monday’s clashes took place a day after 15 inmates were killed during riots at a prison in the state, authorities said.
Those clashes broke out around 11:00am (15:00 GMT) during visiting hours at the facility, located some 28km from the state capital Manaus.
“It was a fight between the inmates. There had never been deaths during the visits,” Colonel Marcos Vinicius Almeida told a news conference on Sunday.
An investigation has been opened to determine the cause of the fight, Almeida said.
Almeida emphasised that authorities had reacted within minutes to the Sunday violence, preventing a potentially worse result.
In January 2017, the same facility was the scene of a prison rebellion that lasted almost 20 hours and left 56 people dead.
Brazil has the world’s third largest prison population, with 726,712 inmates as of June 2016, according to official statistics.
The population is double the capacity of the nation’s prisons, which in the same year was estimated to be 368,049 inmates.
Along with severe overcrowding, Brazil’s prisons are plagued by gang violence, while riots and breakout attempts are not uncommon.