Policeman Cesar Castillo told local radio that two adults and two children were initially wounded in the attack, but one of the adults later died from their injuries at the city hospital some 200 kilometers (124 miles) east of the capital.

According to eyewitness accounts the gunmen hailed the bus to pull over, but then sprayed the vehicle with heavy machine gun fire after the driver failed to stop.

The attack comes just three days after a passenger bus bombing killed seven people in the capital of neighboring Guatemala, where President Alvaro Colom condemned the blast as a "terrorist act" blamed on organized crime groups that operate in Central America.

In Guatemala, Honduras and El Salvador, organized crime syndicates such as Mara 18 or Mara Salvatrucha and the M-19 operate protection rackets and extortion rings, often demanding so-called circulation taxes.