A prison uprising early on Sunday left at least four dead, adding to chaos in Brazil's penitentiary system that has seen almost 100 inmates killed in the past week in a gang war.
The latest violence took place at the Desembargador Raimundo Vidal Pessoa jail in the centre of the Amazonian city of Manaus, according to a report in the Folha de S.Paulo newspaper, citing the state's top security official, Sergio Fontes.
Calls and e-mails to the Amazonas state government, where Manaus is located, were not answered.
In the last week, at least 64 inmates have been killed in prisons in or near Manaus. A prison uprising in the neighbouring state of Roraima left at least 33 dead.
Behind the bloodletting is an escalating feud between Brazil's biggest drug gangs, who ended two decades of an uneasy working relationship about six months ago.
Brazil's most powerful gang, the Sao Paulo-based First Capital Command (PCC) split with the Rio de Janeiro-based Red Command gang when the PCC took over lucrative drug trading routes in Brazil's south-east.
Previously, the two groups worked together to ensure a heavy flow of drugs and arms over Brazil's borders.
Members of the PCC were targeted last Sunday in the first massive slaughter, which left 56 dead, many decapitated and butchered. It was Brazil's deadliest uprising in more than two decades.
It was the North Family gang - allied with the Red Command - who carried out the killings in that riot, authorities said.
Five days later, PCC members killed at least 33 people at a prison in Roraima state, brutal scenes captured on a mobile phone video spread widely on social media, in which the inmates are seen hacking away at bodies as they say it was an act of revenge.
Authorities originally said 31 prisoners died in the Roraima uprising - but revised that figure to 33 after finding two buried bodies on the prison grounds on Saturday.
It was not immediately clear what drug faction - if any - was behind the most recent killing in jail in Manaus.
Experts say the PCC is moving to infiltrate areas in the Red Command's home base of Rio and is infiltrating Brazil's Amazon region in efforts to control cocaine-smuggling river routes.
