RIO DE JANEIRO, May 26 (Xinhua) -- A prison conflict in northern Brazil left 15 dead on Sunday, local authorities confirmed.

According to the authorities, the incident occurred at the Anisio Jobim Prison Complex in the Amazon Rainforest region. It was not a prison riot, authorities said, but a fight between inmates during visit hours.

"There had never been deaths during visiting hours. Some inmates died in their locked cells. The crimes were committed in front of inmates' families," said Marcos Vinicius Almeida, head of the Prison Administration Secretariat.

According to Almeida, the victims were killed by strangulation or stabbed with toothbrushes. No prison wardens were injured during the incident.

The motives for the fight were so far unknown but an investigation will be started. According to the authorities, the cameras in the prison have captured the process.

The Anisio Jobim Prison Complex is the very jail where, in early 2017, a riot resulted in the deaths of 56 people, many of whom were decapitated.