An inmate has been decapitated and five others have also died at a prison in northern Brazil.
The prisoners died at the Unidade Prisional do Puraquequara (UPP) in Manaus, the capital of Amazonas state, and the same prison where four other inmates died during riots in January.
Riots in prisons across Brazil left more than 120 inmates dead, including 50 at another Amazonas jail, in January 2017.
According to the prison administration, there was no riot when the killings occurred on Friday, and inmates did not resist police who responded to the crimes.
The killings at Brazilian prisons in recent months have seen inmates decapitated or dismembered in violence largely blamed on clashes between rival gangs.
Many of the South American country's prisons are overcrowded, understaffed and virtually controlled by gangs.
At the UPP, 1,286 prisoners are being held in a facility built for less than half that number, according to the prisons administration.