Reporting from Mexico City — At least 20 inmates were killed and 12 injured in rioting Saturday at a prison that houses members of drug gangs in the violent border city of Matamoros, authorities said.
Fighting broke out between two inmates, the Tamaulipas state government's public security office said in a statement, and soon dozens more piled on.
Federal and state police were summoned to help guards restore order at the prison, the statement said. News video showed helicopters hovering over the gray watchtower of the prison.
The state public security office did not say how the inmates were killed, what weapons were used or which gangs the prisoners belonged to. Bodies were being sent to forensic officials for autopsies, the statement said.
Matamoros, in Tamaulipas state, sits across the border from Brownsville, Texas. It has been the scene of a deadly battle between the once-dominant Gulf cartel and the powerful Zetas paramilitary gang, vying for control of the valuable drug- and human-smuggling corridor.
Violent riots are common in Mexican prisons, especially those in the north, where members of rival gangs are often jailed in the same overcrowded institution.
Seven prisoners were killed last week in the state of Nuevo Leon, which borders Tamaulipas. In July, 17 were killed in a riot at a prison in Ciudad Juarez, across the border from El Paso.
The prisons also tend to be porous. Hundreds of inmates escaped last year, including 40 from the Matamoros facility in March; 50 guards and the warden were held for questioning.
Last month, 32 prisoners were sprung almost simultaneously from three jails in the coastal city of Veracruz, in a state that also borders Tamaulipas.