Authorities say four bullet-riddled bodies have been discovered at a ranch 30 miles southeast of the northern Mexican border city of Nuevo Laredo.

Meanwhile, four more shooting deaths in two attacks also were reported over the weekend in Nuevo Laredo, across the U.S. border from Laredo.

The four bodies found at a ranch in the rural town of Anahuac included a 13-year-old boy.

Jorge Cantu, a spokesman for the Nuevo Leon state attorney general's office, says the victims had been dead about 36 hours before police found them Sunday.

Cantu says prosecutors were investigating whether killings were related to smuggling after finding soldering and tire-repair equipment on the premises.

Smugglers are known to use tires to sneak drugs across the U.S. border.