At least 25 inmates were killed, including six who were decapitated and burned, in clashes between rival criminal factions at a prison in northeastern Brazil, local media reported.
More than 100 relatives of inmates, mostly women, were taken hostage during the confrontation on Sunday at the Penitenciária Agrícola de Monte Cristo in Boa Vista but were later freed by the police, Globo TV's website G1 cited city officials as saying.
The confrontation was triggered when members of the Primeiro Comando da Capital faction invaded the prison wing where inmates from the Comando Vermelho faction were held, local news website UOL said.
At least six inmates were decapitated and burned, the report added, citing the prison workers' union.
Officials at the city's government did not confirm the number of casualties, according to the report.
The Boa Vista's Justice and Citizenship Secretariat, the prison workers' union and local police could not be immediately reached for comment.
Violent prison fights and riots are common in Brazil's overcrowded prison system, which has long been criticized by human rights organizations for its prison conditions.