The wave of violence blamed for nearly 7,000 deaths in Mexico since late 2006 has claimed over a dozen lives in the last couple of days, EFE news agency reported today.
Police have found two more severed heads from a cooler with a threatening message in Lazaro Cardenas, a port on the Pacific Ocean in western region of Michoacan.
The contents of the message, believed to be from a drug cartel, have not been revealed, an official of the Michoacan state Attorney General's Office said.
Another body with a similar threatening letter was found on Friday from Cuautitlan, Mexico state.
In a separate incident, 10 suspected drug-cartel gunmen were killed and two injured in a shootout with police in Sonora state Friday, said provincial Attorney General's office spokesman Jose Larriñaga Talamantes.
Elsewhere, in the northwestern state of Baja California, four people including a 15-year-old boy lost their lives on Friday when an armed group staged an attack with firearms against a veterinary store in the city of Rosarito, not far from San Diego, California.
Besides the boy, the owner of the veterinary store and two of his employees were killed.
Mexico has been plagued in recent years by drug-related violence, with powerful cartels battling each other and the security forces, as rival gangs vie for control of lucrative smuggling and distribution routes.
Armed groups linked to Mexico's drug cartels murdered around 2,700 people in 2007, and the death toll this year has already topped 4,000, according to unofficial press tallies.
Thousands of federal forces have been deployed nationwide to battle the cartels and part of their task has been to investigate alleged ties between corrupt local police forces and the drug mobs.