Police found the bodies of 16 people dumped in a vehicle on Monday in the southwestern Mexican state of Guerrero, one of the areas worst hit by feuding between drug gangs.
The victims, found near Coyuca de Catalan, on the border with the western state of Michoacan, had been shot and showed signs of torture, local police said.
"We don't yet have information on who these people are. This is a very violent area," a local police official said.
Michoacan is home to the "La Familia" drug gang and its offshoot "The Knights Templar," which have been mired in a bloody struggle for control in the area.
Local media reported "La Familia" had claimed responsibility for the attack with messages daubed onto the vehicle. It was one of the worst killings in Guerrero in recent months.
Home to the popular beach resort Acapulco, Guerrero has suffered one of the highest death tolls in turf wars between Mexico's drug cartels, which have overshadowed the administration of outgoing President Felipe Calderon.
Calderon sent extra reinforcements to Guerrero late last year in an effort to curb the violence blighting Acapulco, and the rate of killing fell during the early months of the operation known as "Guerrero Seguro", or Safe Guerrero.
However, recent weeks have seen a rise in violence again in Guerrero as the centrist Enrique Pena Nieto prepares to succeed the conservative Calderon as president in December.
Pena Nieto has pledged to quickly reduce the violence in Mexico. Killings leapt over the last six years during Calderon's army-led efforts to bring the drug gangs to heel.
More than 55,000 people have died in the drug-related violence in Mexico under Calderon.