Prison clashes between rival gangs killed at least 18 inmates in two penitentiaries in remote parts of northern and western Brazil, including six men who were decapitated and their bodies set on fire, Reuters reported.
About 100 relatives of inmates were taken hostage in the first clash on Sunday in Boa Vista, in the northern state of Roraima bordering Venezuela, in which 10 prisoners died, officials told Globo TV's website G1.
The hostages were later freed by police, according to G1, which earlier had reported 28 dead in the facility.
Eight inmates died and two were injured in another clash between gangs early on Monday in the state penitentiary in Porto Velho, a western city on the border with Peru.
The dead were asphyxiated by smoke when inmates set fire to mattresses, prison director Jobson Bandeira told G1.
In a separate uprising in a penal facility for psychiatric patients, inmates burned to the ground a wing of the prison and began to escape, G1 reported. Police used helicopters to chase the escapees. No deaths were reported.
Violent fights and riots are common in Brazil's overcrowded prison system, which has long been criticized by human rights organizations for its bad conditions.