A total of 12 state and municipal policemen were ambushed and killed on a highway in southern Mexico's Guerrero state between Sunday night and early Monday, authorities announced Monday.

Local Security Force spokesman Arturo Martinez Nunez said a group of policemen were ambushed by a group of armed people on a road of the municipality of General Canuto Neri, leaving 12 people dead and 14 others wounded.

Martinez said the police were investigating the death of 10 beheaded people whose head were dumped earlier Sunday when they were attacked.

The heads of seven men and three women were found Sunday morning outside a slaughterhouse in the same municipality, a village located in an inaccessible mountain, where drug cartels fight for control of criminal activities.

The heads were found left with a message related to the La Familia drug cartel. La Familia is a violent criminal organization that is waging a bloody fight against another group of the Knights Templar in the neighboring state of Michoacan and part of Guerrero.

More than 47,000 people have been killed in drug-related violence in Mexico since President Felipe Calderon launched the " war against organized crimes" in 2006.