On Wednesday, gunmen killed 24 people at a drug rehabilitation facility in the central Mexican city of Irapuato.
The attack occurred in the north-central state of Guanajuato.
At least seven people who were shot were seriously injured.
No motive was given in the attack, but Governor Diego Sinhue said drug gangs appeared to have been involved.
“I deeply regret and condemn the events in Irapuato this afternoon,” Sinhue wrote. “The violence generated by organized crime not only takes the lives of the young, but it takes the peace from families in Guanajuato.”
Police in a statement said the drug rehabilitation facility was not formally registered.
Attorney General Carlos Zamarripa said he had designated a specialized team to investigate the killing, which he called a “cowardly criminal act,” while Governor Sinhue called for a joint effort from federal and state authorities to tackle violence.
This is the deadliest attack on a rehab center in over a decade. In 2010, 19 people were killed in Chihuahua city in northern Mexico. Since then over a dozen attacks on such facilities occurred.
Drugs are a big problem in Mexico. Often dealers who could face attacks from rivals take refuge at such private run facilities.