MEXICO CITY – Suspected drug hitmen attacked a group of sleeping soldiers with grenades in central Mexico, sparking a battle that killed three gunmen, a state attorney general's office said Wednesday.

Around 15 drug gangsters in vehicles surprised the soldiers while they were camped out in the central state of Guanajuato Tuesday night, shooting at them with automatic weapons.

“Two soldiers were injured in the clash in a firefight that lasted several minutes,” a spokesman for the Guanajuato state attorney general's office said.

Guanajuato state is famed for its beautiful historic state capital popular with U.S. and European tourists, but drug violence is creeping up in the once quiet area as drug gangs fight over smuggling routes to the United States.

More than 2,300 people have been killed in drug violence across Mexico this year, a faster rate than in 2007, as Mexico's most-wanted man, Joaquin “Shorty” Guzman, vies with rivals for control of the country's lucrative drug trade.

President Felipe Calderón has made crushing drug gangs the main goal so far of his six-year term, sending troops across Mexico on taking office in December 2006.

But drug violence has spiraled as rival gangs fight each other and the army. Endemic police corruption has further complicated efforts to rid Mexico of cartels.

(Editing by Sandra Maler)