REYNOSA, Tamaulipas – Mexican authorities are investigating the local kidnapping of 19 victims after a bus hijacking by cartel gunmen. The scene of the incident sits within contested territory of rival Gulf Cartel factions.

The kidnapping occurred Sunday afternoon along the highway that connects Matamoros and Reynosa, near the rural community of Palos Blancos. According to Mexican federal law enforcement sources, a bus from the company Transpais was originally traveling to Reynosa from Tampico.

Four SUVs with cartel gunmen pulled up to the bus and forced it to stop, according to initial information provided by law enforcement sources. Four gunmen wearing masks boarded and removed 19 men before fleeing the scene. The bus originally carried 41 passengers and arrived in Reynosa with 22. One of the theories under consideration is that the victims were migrants trying reach the U.S. border and were kidnapped by a Gulf Cartel faction after their smuggler failed to pay the needed protection fees. Another theory suggests the migrants were leveraged to extort additional funds from relatives.

The scene of the kidnapping is located in a contested region between rival factions of the Gulf Cartel. The ongoing violence has led to hundreds of murders, large-scale gun battles, and kidnappings as the two groups fight for territorial control.