Police have found the charred remains of 14 bodies in a mass grave in central Mexico, victims of drug hitmen fighting over smuggling routes into the United States, an attorney general's office said on Wednesday.

Soldiers and investigative police found the bodies, mainly bones and badly burned remains, outside a drug safe house after a raid last week in the town of Apaseo el Alto in the once quiet state of Guanajuato.

Security forces came under heavy fire during the raid and killed 12 hitmen that authorities said were working for the armed wing of Mexico's Gulf cartel, the Zetas.

"We have found the remains of 14 bodies buried in the garden of the safe house and who we believe were killed by the Zetas," said a spokeswoman for the Guanajuato attorney general's office.

Rival gangs have taken their fight over Mexico's $40 billion-a-year drug trade inland as they battle for cocaine smuggling routes running up from Central America into the world's top drug consumer, the United States.

Officials in Guanajuato say the Gulf cartel, known for its brutality and for beheading its rivals, is fighting a group of smugglers from the western state of Michoacan called "La Familia" (The Family) for control of the state.

President Felipe Calderon has sent thousands of troops across Mexico to rein in the cartel turf wars. But drug-related violence has surged, killing 12,300 people since he took office in December 2006.

The drug war is a major concern for voters who mainly support Calderon's efforts but are fearful of the growing insecurity and for investors and Washington as the Mexican government struggles to cleanse police forces of corrupt officers working for gangs.