Gunmen shot dead 11 people and wounded at least nine others at a rehab center in northern Mexico on Sunday in the latest bloody episode in a brutal turf war between drug gangs.

Dead bodies were strewn across blood-soaked beds, armchairs and the floor at the church-operated rehabilitation center in the city of Torreon, the Milenio television network reported.

"The armed attackers came on two pickup trucks, entered the center and opened fire," a senior police official told AFP on condition of anonymity.

The attack came almost a year to the day after a similar assault on a rehab center downtown left 11 people dead and wounded two others.

Five drug rehabilitation centers - all in the north of the country - were attacked in 2010. In one of the worst attacks, again in June, some 30 gunmen stormed a facility in the city of Chihuahua, killing 19 people.

These centers have become frequent targets of drug cartels, which seek members of rival trafficking groups among the patients and eliminate them to prevent them from talking to the police.

The latest assault on the Torreon center, called "Your Life on the Rock," occurred at 9:15 pm Sunday (0215 GMT Monday).

The gunmen used AR-15 assault rifles and nine-millimeter caliber pistols, police said. According to eyewitnesses, some victims walked away before the authorities arrived. The dead have not yet been identified.

The building, located in a residential area in front of a park, was cordoned off by police and forensic experts were working on the crime scene.

The army and police established security checkpoints around the hospital where the wounded were being treated in order to prevent contract killers from finishing off those who survived the attack.

Police also stepped up patrols around the city of one million inhabitants, located some 550 kilometers (350 miles) from the US border city of Laredo, Texas.

More than 50,000 people are believed to have been killed in drug-related violence in Mexico since 2006.

That year the government launched a military crackdown on the country's powerful drug cartels, which are themselves locked in brutal turf wars marked by macabre displays of violence such as beheadings and mass graves.

The Torreon region is a scene of a violent confrontation between the Sinaloa cartel and the Zetas, an increasingly powerful drug trafficking group founded by deserters from US-trained Mexican special forces.

The two gangs are fighting for control of lucrative cocaine delivery routes to the United States.

Across the border, five bodies burnt beyond recognition were found over the weekend in the smoldering wreckage of a vehicle on a popular drug trafficking route in the Arizona desert.

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