At least 20 people were killed during a clash between drug cartels in the Sothern Mexican state of Chiapas, the latter’s public security service said, reports Excelsior newspaper.

The armed conflict took place on June 29 in the city of La Concordia.

Law enforcement officers who arrived at the scene of the incident found a pickup truck with 15 dead bodies in its body. Two others were found inside the vehicle, and three other—next to this SUV. All had died from gunshot wounds. Documents from Guatemala, bordering Chiapas, were found in the possession of four of the dead.

According to preliminary data, the armed conflict was the result of a confrontation between the Sinaloa cartel as well as the Chiapas and Guatemala cartels for the right to control the border area.