Ten people were killed in an attack Saturday on a drug rehabilitation center in the central Mexican state of Guanajuato, local authorities said.
An armed group stormed the center in Irapuato in the afternoon and opened fire, killing nine people instantly, the municipal government said.
A 10th person was wounded but later died in hospital, the state secretariat of public security said.
"The attackers entered the place with great violence," the authorities said.
Police arrived to safeguard the scene and officers from the state prosecutor's office later collected evidence to start the preliminary investigation.
Guanajuato is an important industrial center in Mexico, hosting major international manufacturers of automobiles, aircraft and other heavy industry.
These activities, along with the presence of important energy infrastructure, have attracted two major cartels which are engaged in drug trafficking, extortion and kidnapping.
Mexico last year registered a record 34,582 intentional homicides, the highest since official records started in 1997.