At least 14 men have been killed and their bodies left in a Mercedes Benz van on a major highway in Mexico's central state of San Luis Potosi, a prosecutor said.
The men were kidnapped on Wednesday in the northern state of Coauhuila, where the vehicle was stolen in an armed robbery, an official from the attorney general's office of San Luis Potosi said.
The corpses were found early on Thursday morning.
Gabriela Gonzalez, a spokeswoman for the prosecutor's office, told the AFP news agency by telephone on Thursday: "According to the initial information, everything indicates that it was the work of organised crime."
The bodies were found at around 4:30am local time, 9:30 GMT near a fuel station on the outskirts of San Luis Potosi, capital of the state.
The victims were then believed to have been taken to the state of Zacatecas, before being killed and dumped in San Luis Potosi.
The vehicle they were found in had been reported stolen in Coahuila.
Gonzales was unable to say whether the men died of gunshot wounds, or some other cause.
It was the first time San Luis de Potosi has been a scene of a massacre on this scale, although US immigration agent Jaime Zapata was killed and another agent wounded in an attack there in February 2011.
Zapata's murder has been attributed to the Zetas crime group, one of the country's most feared, which is known to operate in Coahuila and Zacatecas.
Renewed turf war
Mass killings, with the bodies abandoned inside cars or dumped on the side of the road, have multiplied in Mexico since 2011, but have been seen mainly in the states of Veracruz and Tamaulipas.
The most recent occurred on June 12 when 14 bodies were found in a vehicle in northern Veracruz near the border with Tamaulipas.
On May 13, 49 bodies were found in the community of Cadereyta in Nuevo Leon state. They had been decapitated and their hands had been cut off.
More than 50,000 people have been killed in drug-related violence since 2006 when then president Felipe Calderon ordered the military take the lead in a war against the country's powerful drug cartels.
A study released on Thursday by Lantia Consultores estimated that more than 7,000 murders linked to organised crimes were carried out in the first half of 2012 - a 10 per cent increase over the previous six-month period.
It attributed the increase to a reactivation of a turf war between the Zetas and the Sinaloa cartel.
Meanwhile in other violence, unidentified assailants in two vehicles opened fire on the offices of El Regional Sur newspaper in Cuernavaca, 90km south of Mexico City.
It was the fifth attack in a month on offices of a news organisation in Mexico.