Mexican authorities say nine people were killed and a child wounded in two gunbattles in the northern border state of Sonora.

State prosecutors say in a statement Tuesday that the first firefight took place the previous afternoon in Agua Prieta, which lies across the border from Douglas, Arizona. Four men and a woman were found dead in two cars and lying on a street. Some were clad in tactical vests, and assault rifles were recovered at the scene.

About two hours later, more gunfire erupted on a highway in nearby Naco. Four men were found shot dead in a car with Arizona license plates. A 12-year-old boy was wounded by a stray bullet but his life was not in danger.

Police were investigating whether the incidents were linked.