A total of 24 people were killed and seven others injured as gunmen burst into an unregistered drug rehabilitation center in central Mexico and opened fire on Wednesday.
Police in the north-central state of Guanajuato said the attack occurred in the city of Irapuato. Three of the seven wounded were reported in serious condition.
The attackers apparently shot everyone at the rehab center, said the State police adding that nobody was abducted.
Photos purporting to show the scene suggest those at the center were lying down when they were sprayed with bullets.
Guanajuato is the scene of a bloody turf battle between the Jalisco cartel and a local gang, and the state has become the most violent in Mexico.
Governor Diego Sinhue Rodríguez Vallejo said drug gangs appeared to have been involved.
“I deeply regret and condemn the events in Irapuato this afternoon,” the governor said. “The violence generated by organized crime not only takes the lives of the young, but it takes the peace from families in Guanajuato.”
In the past, Mexican drug gangs killed suspected street-level dealers from rival gangs sheltering at such facilities.
However, it was one of the deadliest attacks on a rehab center since 19 people were killed in 2010 in Chihuahua City in northern Mexico. More than a dozen attacks on such facilities have occurred since then.
Mexico has long had problems with rehab centers because most are privately run, underfunded and often commit abuses against recovering addicts. The government spends relatively little money on rehabilitation, often making the unregistered centers the only option available for poor families.