Gunmen Kill 13 at Drug Rehab Center in Mexico

MEXICO CITY -- Mexican authorities say two men who were wounded during an attack on a drug rehabilitation center in the northern city of Torreon have died, raising the number of fatalities to 13.

Coahuila state prosecutors say in a statement issued Wednesday that two assailants stormed into the center Tuesday afternoon and opened fire.

Officials say it is not yet clear what the motive for the attack was or which gang was responsible.

Drug cartels are known to use rehab centers to recruit addicts and rival gangs sometimes attack.

Dozens of people have died in shootings at centers across Mexico. The worst incident left 19 people dead in Chihuahua city last summer.