An attack by members of one crime gang on rival inmates touched off a riot at a prison in the northern state of Amazonas, leaving at least 56 dead. The riot that erupted from Sunday afternoon into Monday morning developed out of a fight between two of the country's biggest crime gangs over control of prisons and drug routes in northern Brazil.

In a separate incident Monday evening, four inmates were killed at another Amazonas prison. Police were investigating whether there was a connection between the mass killings at the Anisio Jobim Penitentiary Complex and the later ones at Unidade Prisional do Puraquequara.

There were 1,224 inmates in the prison, which was built to hold 592. The prison is run by a private company that is paid according to the number of inmates.

Reports state that many of the dead had been beheaded. Judge Luis Carlos Valois, who negotiated the end of the riot with inmates, said he saw many bodies that had been quartered.