A drug gang kidnapped and killed six people near a town in the U.S.-Mexican border region Tuesday, prompting a series of gunbattles with soldiers that left 15 others dead.

The violence started when gunmen kidnapped nine alleged members of a rival drug gang in Villa Ahumada and later executed six of them along the PanAmerican highway outside of the town, 80 miles south of Ciudad Juarez, across the border from El Paso, Texas, said Enrique Torres, spokesman for a joint military-police operation in Chihuahua state.

Assailants later released three of the men, although their whereabouts was not immediately known, Torres said.

Soldiers later caught up with the gunmen and a series of shootouts ensued, leaving 14 alleged gunmen and one soldier dead Tuesday, Torres said. Another soldier was wounded.

Mexico has been besieged by drug violence amid a two-year government crackdown. President Felipe Calderon said Monday that more than 6,000 people have died in drug-related violence.

Villa Ahumada, a town of 1,500 people, was virtually taken over by drug gangs last year when gangs killed two consecutive police chiefs, and two officers. The rest of the 20-member force resigned in fear, forcing the Mexican military to take over for months until the town was able to recruit new officers.

The town's mayor, Fidel Chavez, fled to the state capital for his own safety.

Also Tuesday, Tijuana city police said emergency officials responding to a report of a car on fire found a sport utility vehicle engulfed in flames and two charred bodies inside.

And in Tepotzotlan, a small town outside Mexico City, two heads in coolers were found inside a car, according to an official with the Mexico state prosecutor's office, who was not authorized to give her name. The heads were accompanied by a message threatening the municipal police chief. Decapitations have become commonplace in Mexico's drug violence.

In other violence late Monday, armed men forced their way into a Mexican prison in Torreon, then killed three prisoners by beating them and setting them on fire in a bathroom. The assailants also freed nine inmates before escaping, state prosecutors said in a statement Tuesday.

Fighting between rival gangs left another two inmates dead Tuesday at an overcrowded prison in central Mexico, said Carlos Gil Abarca, a spokesman for the prevention and rehabilitation office of the Mexico state government.