Mexico ? An explosion at a plaza in northeastern Mexico injured 15 people, an attack authorities blamed Sunday on drug cartels targeting the civilian population to cause chaos.

Police believe the attackers threw a grenade Saturday night at the main square in the town of Guadalupe, but were still trying to confirm the type of explosive, said Adrian de la Garza, the director of the investigations agency of Nuevo Leon, where the town is located.

Six children, the youngest 3 years old, were among the injured, said Francisco Gonzalez, the state deputy health director. He said the injuries were not life-threatening, and most of the victims had returned home from the hospital.