Armed assailants kill 11 people at a soccer field in Salamanca, Mexico.

According to Salamanca’s mayor, Cesar Prieto, a group of armed attackers opened fire at a soccer field after a match in the Mexican city, killing 11 people and injuring 12 others. The incident was shared on Facebook on Sunday, though the motive remains unknown.

A woman and a child were among those injured in the “regrettable and cowardly” attack in the Loma de Flores community during a social gathering, Prieto added, describing the incident as a severe social breakdown.

“This incident adds to a wave of violence that we are sadly experiencing in the state, and particularly in Salamanca,” he added. “Unfortunately, criminal groups are trying to subjugate the authorities, which they will not achieve.”

An investigation has been launched into the attack, said the office of the attorney general in the state of Guanajuato, where Salamanca is located.

The office was coordinating efforts with municipal, state and federal authorities to strengthen security in the area, protect its people and find the likely perpetrators, it added in a statement.

“Those responsible will be found,” Prieto said in his Facebook post.

Guanajuato is one of the most dangerous states in Mexico.