Eight men were killed on Thursday morning at a house in the northern Mexican city of Monterrey, the third largest city in Mexico, local authorities said.

Police sources said the incident occurred shortly after 6 a.m. (1200 GMT) when neighbors heard detonations of caliber weapons. Military forces as well as state and municipal police then rushed to the scene.

Shell cases from guns and AK-47 rifles were found in the house. The victims, aged between 20 and 30, had shots in their heads, the sources said.

Battles between drug traffickers for control of criminal activities in some states, especially those in the northeast and the east, have generated waves of violence. Over 1,600 were killed in 2011 in Nuevo Leon state.

More than 45,000 people have been killed in drug-related violence in Mexico since President Felipe Calderon launched the "war against organized crimes" in 2006.