Six severed heads were discovered on a roadside in central Mexico early Tuesday, in a region that is generally considered peaceful and not known for frequent cartel violence.

Authorities confirmed the shocking find on a road connecting the states of Puebla and Tlaxcala.

Police did not immediately give a motive or identify which of the criminal groups operating in Mexico may have been responsible. Local reports said a blanket was left near the scene with a message threatening rival gangs and signed by a group calling itself "La Barredora," meaning "the sweeper."

It remains unclear whether the group behind the signature is linked to the small criminal organisation of the same name known to operate in Guerrero, or why they would target this area.

The state prosecutor’s office said the remains belonged to men and announced the opening of an investigation. According to AFP, the authorities are working to determine both the identities of the victims and those behind the killings.

The discovery comes at a time when Mexico is facing multiple security challenges. In addition to the long-running issue of drug trafficking, the region also struggles with large-scale fuel smuggling, known locally as "huachicolea," which is worth billions of dollars to criminal organisations.

Federal authorities have not issued a response to the killings.

The case unfolds as President Claudia Sheinbaum’s administration intensifies its crackdown on fentanyl trafficking.

While Puebla and Tlaxcala are not usually hotspots for cartel violence, the brutal discovery has raised alarm.

Other regions have seen frequent bloodshed: in June, 20 bodies were found in Sinaloa, four of them decapitated, while in May, seven youths were killed during a church festivity in Guanajuato.

Mexico has endured rising levels of gang violence in recent years, with hundreds of thousands killed and tens of thousands missing since the government launched its military-led campaign against cartels in 2006.