Police say a fight between inmates at a prison in the Mexican border city of Ciudad Juarez has left at least 20 prisoners dead.

Chihuahua state police spokesman Carlos Gonzalez says a fight broke out between three different gangs about 6 a.m. yesterday at the state prison in the city across the Rio Grande from El Paso, Texas.

About 200 anti-riot police and 50 soldiers regained control of the prison three hours later.

Gonzalez says authorities are investigating why the rival gangs were in the same area in violation of policy.