Though the victims were yet to be identified, police believe they may include Mexicans, Guatemala or Colombians, he said.

Officials said, the bruise marks on the bodies suggested they were tortured before being killed by shooting to the back of thier head from a close range.

Meanwhile, police in the northern state of Nuevo Leon have also found two burned human heads on a road in the city of Escobedo, the state Attorney General’s Office said.

An anonymous caller tipped off authorities to the location of the human remains, the AG’s office said, adding that the condition of the heads made it impossible to determine the gender or age of the victims.

On Sunday, the decapitated bodies of eight army soldiers were found along an urban boulevard in the southern state of Guerrero.

Brutal slayings by drug cartels are on the rise in Mexico, and officials estimate that more than 5,300 people have died in organized crime-related slayings this year.

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 1,500 in 2006, with the death toll this year already at more than 5,300, according to governemnt data.

The wave of killings began last Wednesday, when three soldiers were stabbed to death inside a Monterrey bar.

An army veteran met the same fate last Thursday, the same day troops operating in Nuevo Leon seized nine tonnes of marijuana and an arsenal of guns and ammunition in the course of five separate battles with drug-cartel gunmen.

On Friday, four soldiers were found beheaded, two of them in a spot near one of the previous day’s clashes between the army and cartel-hired gunmen.

Nuevo Leon, which borders Texas, has logged nearly 150 killings in recent months as rival drug traffickers vie to control smuggling routes and local retail sales of pot, cocaine and other drugs.

The US Consulate in Monterrey suspended operations last Thursday after unknown assailants shot out some windows and hurled a grenade that failed to detonate.

Separately, a Mexican Federal Police officer was gunned down early Monday in Ensenada, a city about 116 km south of Tijuana in the northwestern state of Baja California, authorities said.

His death followed the murders of 10 people, including two other police officers, in Baja California in a 24-hour period last weekend.

The two police officers were killed in a hail of gunfire in Playas de Rosarito, which is near Tijuana, while the other bodies were found in and around the border city.

Mexico has been plagued in recent years by drug-related violence, with powerful cartels battling each other and the security forces.

Armed groups linked to the cartels murdered around 2,700 people in 2007, and the death toll this year has already touched 4,000, according to unofficial press tallies.