Police found 14 bodies in an abandoned van Thursday in northern Mexico, officials said, in what appeared to be the latest in a series of grisly killings linked to the country's brutal drug war.
Meanwhile in the restive northwestern state of Sinaloa, gunmen opened fire with AK-47 assault rifles on a house party late Wednesday, killing seven people, police said. The victims were all men aged 46 to 76.
Sinaloa is a stronghold of the cartel of the same name led by powerful drug lord Joaquin "El Chapo" Guzman, and one of the states hit hardest by the cartel battles over territory and trade routes to the lucrative US market.
Gabriela Gonzalez, a spokeswoman for the prosecutor's office, said the 14 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 state 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 organized crime," Gonzalez told AFP by telephone. She 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 feared Zetas crime group, known to operate in Coahuila and Zacatecas.
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 President Felipe Calderon ordered the military to take the lead in a war against the country's powerful drug cartels.
A study released Thursday by Lantia Consultores estimated that more than 7,000 murders linked to organized crimes were carried out in the first half of 2012 -- a 10 percent increase over the previous six-month period.
It attributed the increase to a renewed turf war between the Zetas and the Sinaloa cartel.
In other violence on Thursday, unidentified assailants in two vehicles opened fire on the offices of El Regional Sur newspaper in Cuernavaca, 90 kilometers (55 miles) south of Mexico City.
It was the fifth attack in a month on the offices of a news organization in Mexico.