MEXICO CITY (AP) -- Police found the mutilated bodies of 13 people inside two vehicles abandoned in separate towns of the northern border state of Tamaulipas, an official said Friday.

Authorities first found the cut-up bodies of two women and three men late Thursday in a potato chip delivery truck abandoned in the parking lot of a supermarket in the town of El Mante, a Tamaulipas state official said. He spoke on condition of anonymity because he was not allowed to talk about the case.

The official said police also found a threatening message allegedly signed by the Gulf drug cartel.

An hour later, police found eight bodies in the town of Soto la Marina along with a message alleging the victims were members of the Gulf cartel.

Northeastern Mexico along the border with Texas has been a war zone of shootouts and gruesome mass killings as the Zetas and Gulf drug cartels battle each other in the states of Coahuila, Nuevo Leon and Tamaulipas - a region that is home to cattle ranches, sorghum fields and the industrial city of Monterrey. The Zetas were hit men for the Gulf cartel until they split in 2010, unleashing their bloody war.

In Coahuila on Friday, police found the bodies of four men hanging from a highway overpass in the capital city of Saltillo.

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