Four inmates were killed and five wounded in a battle between rival youth gangs at a Guatemalan youth prison, police said.
One of the victims was shot dead in a prison dormitory and two others were beaten to death with concrete blocks after their hands were cut off. "They destroyed their faces completely. There are body parts everywhere," a police said.
A fourth prisoner died of a bullet wound to the head after being rushed to the hospital.
About two dozen surviving prisoners lay face down on the prison grounds after police regained control of the prison, where 12 were killed in a gang massacre last year.
The gangs, or "maras", have their roots in Los Angeles and have spread rapidly across Central America in recent years.
The largest gangs, Mara Salvatrucha and Mara 18, regularly attack each other in prisons and on the streets of Guatemala, El Salvador and Honduras.