Twelve men were decapitated and dumped at separate sites in the southern Mexican state of Guerrero, authorities said Sunday.
Mexican news outlets quoted Guerrero Gov. Zeferino Torreblanca Galindo as saying that eight of the men were identified as Mexican soldiers and another as a former state police commander. Earlier, Mexican media had said that the victims' close-cropped hair indicated they were soldiers.
Nine of the heads and bodies were discovered Sunday in the city of Chilpancingo, the state capital. The heads were bundled in a plastic bag and dumped at a shopping center, and the bodies turned up in two other locations at opposite ends of the city, authorities said.
Local prosecutors said three more decapitated bodies were found in a village on the outskirts of the city, the Associated Press reported.
The find came two days after three gunmen were killed in a shootout with soldiers in Guerrero. Mexican media said the beheadings may have been intended as retribution.
The website of the daily El Universal newspaper, citing unnamed state law enforcement officials, reported that a message that accompanied the bag of heads warned: "For every one of mine you kill, I'm going to kill 10 of yours."
Beheadings have become increasingly common around Mexico amid rising drug-related violence that has killed more than 5,300 people this year.
President Felipe Calderon launched a crackdown against drug traffickers upon taking office two years ago, triggering clashes between security forces and gunmen and vicious feuding among rival drug gangs.
The coastal state of Guerrero, home to the Acapulco resort, has been one of the drug war's more violent corners. Nearly 500 people have been killed there since January 2007, a month after Calderon announced his anti-crime offensive, according to a tally by the University of San Diego's Trans-Border Institute.
As part of his crackdown, Calderon has sent 45,000 soldiers and 5,000 federal police into the streets across the country. The offensive has produced thousands of arrests and some major seizures of drugs, cash and weapons, though there is no sign that any of the main drug gangs have been dislodged.
Most of the killings have resulted from turf wars among drug-trafficking organizations, which battle for the most coveted routes for smuggling into the United States.