DURANGO, Mexico -- Two gunmen stormed into a drug rehabilitation center in the northern city of Torreon on Tuesday, killing 11 people and wounding two.
The Attorney General's Office in Coahuila state said the motive for the attack or the gang responsible were not clear yet.
Drug cartels are known to use rehab centers to recruit addicts, leading rival gangs to attack the centers. Dozens of people have died in shootings at centers across Mexico. The worst incident left 19 people dead in Chihuahua city last summer.
Other attacks at drug centers have taken place in Ciudad Juarez, across the border from El Paso, Texas, and in the northern state of Durango. Both areas have been plagued with violence since President Felipe Calderon launched an offensive against drug cartels when he took office in December 2006.
More than 35,000 people have been killed in drug-related violence across Mexico since then.
Recently, grisly discoveries of mass graves have horrified Mexicans.
The Mexican government said Tuesday that it has unearthed 429 bodies since April from a series of clandestine graves in the northern states of Durango and Tamaulipas.
Police found 236 bodies in Durango's state capital, which is also named Durango, federal Attorney General Marisela Morales said. The remains appeared to be victims of a battle for power within the Sinaloa drug cartel, she said.
Morales said an additional 193 corpses have been found in the town of San Fernando in Tamaulipas state, 85 miles from the U.S. border (136 kilometers). Officials said most of those were Mexican migrants heading to the United States who were kidnapped off buses and killed by the Zetas drug cartel.
The attorney general released the new body count Tuesday.