Police in southern Mexico found two piles of decapitated bodies containing the remains of 11 men.
Photos of the crime scene showed headless corpses stacked on top of one another in a field outside the city of Merida.
Some of the bodies had tattoos and were jumbled amid blankets. The heads were not immediately found.
It appeared to be the largest single group of beheadings in recent years in Mexico.
The tactic has become more frequent in gangland-style killings, and the largest previous instance of decapitations occurred in 2006, when gunmen tossed five human heads into a bar in central Mexico.
The federal attorney general's office confirmed there were 11 dead and it was taking over the investigation - a move that usually indicates a case involves high-calibre weapons or drug trafficking.
Merida, located on the Yucatan Peninsula, has largely been spared the drug-gang violence afflicting many other Mexican cities.Reuse content