Updated

Gang members staged simultaneous riots in at least seven Guatemalan prisons on Monday, attacking rivals with grenades, guns and knives in coordinated chaos that left 31 inmates dead, officials said.

The riots apparently began with attacks by members of the Mara Salvatrucha (search) gang against rivals of the MS-18 gang (search), said Interior Minister Carlos Vielmann.

He said 31 inmates died before the riots were brought under control shortly after noon.

An Associated Press photographer saw 18 bodies, many riddled with bullet wounds, carried from El Hoyon prison (search), which was specifically built to hold gang members in Escuintla, 30 miles south of the capital. A guard and 61 inmates were injured at El Hoyon, and tattooed gang members bleeding from knife wounds were carried from the prison on stretchers.

Escuintla Gov. Luis Munoz said the riot began with the explosion of two grenades.

As explosions echoed from inside the small, converted police barracks in downtown Escuintla on Monday morning, nearby storekeepers rattled metal shutters down over the shop windows and crowds of visitors pressed police for information.

The explosions stopped within an hour. Police first began removing the injured, then the dead.

Dozens of relatives, many of them the mothers of young gang members wept hysterically as stretchers were carried from the prison. The dead were taken to a morgue. So many were injured that they overflowed the capacity of the two local hospitals, forcing officials to take some elsewhere.

Vielmann said visitors had brought guns into the prisons. "Until we have finished the high-security prisons (now under construction), that problem will persist," he said.

Speaking about the apparent coordination of the attacks, Vielmann said, "the gangs maintain constant communication. They have a Web page and not only synchronize in Guatemala, they synchronize with El Salvador, Honduras and with the United States."

He said they also use cellular phones and messages passed by prison visitors.

Human Rights Prosecutor Sergio Morales said there was evidence that police had helped gang members smuggle weapons into El Hoyon.

El Hoyon holds 400 alleged gang members. It which was opened at an old police barracks after a December 2002 riot involving gang members at another prison in which 14 inmates died.

In the other riots Monday, three inmates died Monday at the Canada Prison Farm 12 miles further south, and officials said eight died in rioting at Guatemala's top-security Pavon prison, about 15 miles east of the capital.

Two others were stabbed to death at a prison in Mazatenango, 85 miles southwest of the capital, according to officials.

Vielmann said smaller disturbances were quashed at three other prisons.

Law enforcement officials say the gangs emerged in Los Angeles and later spread to Central America when criminal migrants were deported back home.

Governments throughout Central America have been waging a campaign against the Mara Salvatrucha and related gangs, tightening laws and throwing thousands of the tattooed gang members into prisons, which have often seen clashes between feuding factions.

In May 2004, a fire swept through a prison in San Pedro Sula (search), Honduras, killing 107 inmates, most of them Mara Salvatrucha members.

That fire came 13 months after some suspected gang members were locked in their cells, doused with gasoline and set ablaze during a riot at the El Porvenir prison farm near the Honduran city of La Ceiba. Nearly 70 people, including prisoners, visitors and guards, were killed.

In El Salvador, riots broke out in February when an alleged gang member was transferred to a top-security facility, and one inmate was killed. In September, 800 gang members rioted at two Salvadoran prisons.