At least 12 youths have been killed in an assault on a youth detention facility in Guatemala City.
At least 10 youths were injured in the fighting
Officials said members of a gang, armed with grenades and assault rifles, had raided the centre to attack members of a rival group.
It is the latest in a series of deadly clashes between Guatemala's two main gangs: Mara 18 and Mara Salvatrucha.
The maras emerged in Los Angeles in the 1980s and spread to Central America when gang members were deported.
Officials said members of the Mara Salvatrucha had carried out a "commando-style raid" to force their way into the detention centre.
Once there, they opened fire on members of the Mara 18 being held there.
The attack was described as a "commando-style raid"
Two of the dead had their heads blown off.
At least 10 gang members were wounded in the fighting, some of them seriously.
In a separate incident, three prisoners were shot and beaten to death in a jail in the city of Puerto Barrios.
Feuding between the two maras at detention centres has killed dozens of people in recent months.
In August, 35 people were killed in clashes between the two gangs at a number of prisons.
After the killings, the Guatemalan authorities promised to impose stricter controls in jails, but also acknowledged that the prison system was close to collapse.
The maras were formed in the early 1980s by Salvadorean immigrants who had fled the civil war and settled in Los Angeles.
They were later joined by Hondurans, Guatemalans and other migrants. Many of them were deported back to their countries when Central America's civil wars ended.
Now Honduras, El Salvador and Guatemala are struggling to contain the activities of the maras, which are blamed for a wave of killings and robberies across the region.