Police have found the bodies of 14 men stuffed into an abandoned van near a gas station in northern Mexico.
Gabriela Gonzalez, a spokeswoman for the prosecutor's office in San Luis Potosi state, said the victims found outside the northern city of San Luis Potosi were likely kidnapped as part of a standoff between drug traffickers in the state of
Coahuila, which borders San Luis Potosi and the US state of Texas.
The victims are believed to have then 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.
"According to the initial information, everything indicates that it was the work of organised crime," Gonzalez told AFP by telephone. She was unable to say whether the men died of gunshot wounds or some other cause.
It is the first time San Luis de Potosi has been a scene of a massacre on this scale.
The bodies were discovered on Thursday after police received an anonymous tip, she said.
San Luis Potosi has been the scene of turf battles between the Zetas gang and allies of the Sinaloa drug cartel.
The groups split in early 2010, setting off a bloody battle for territory in northeastern Mexico. Another group, the Sinaloa cartel, later joined the fight as a Gulf Cartel ally.
Also in Mexico's north, attackers armed with assault rifles killed seven men drinking at a sports field on Wednesday night, Sinaloa state prosecutors said in a statement.
The men had just finished working and had gathered at the field to drink when they were attacked, the statement said.
Mexico has seen a growing number of mass killings, with the bodies abandoned inside cars or dumped on the side of the road, most in the states of Veracruz (east) and Tamaulipas (northeast).
Last month, 14 bodies were found in a vehicle in Veracruz.
Another 49 were found in Nuevo Leon state in May. They had been decapitated and their hands had been cut off.
More than 50,000 people have been killed in drug-related violence since late 2006, when Felipe Calderon, Mexico's president, ordered the military to take the lead in a war against the country's powerful drug cartels.