Mexico City - Twelve people were killed in the southern Mexican state of Guerrero in a clash between the military and suspected drug traffickers just hours ahead of US President Barack Obama's visit to the country on Thursday.

Guerrero's Public Security Minister Juan Heriberto Salinas Altes confirmed the deaths late Wednesday. He said the clash happened when a military patrol was attacked near San Nicolas del Oro.

The attackers were armed with rifles, police said. Several managed flee on vehicles they had been using in the region's dirt roads, they added.

Obama was set to arrive in Mexico City on Thursday, for a brief visit focused on the fight against drug gangs.

Drug-related violence has left well over 7,000 people - including hundreds of military and police officers - dead in Mexico since the start of 2008. (dpa)