The severed heads of six men were discovered on Thursday atop a car in a town in southwestern Mexico with a sign warning others they could face the same fate, authorities said, a grisly reminder of the gang violence plaguing the country.

A statement from the attorney general's office of the state of Guerrero said the remains were found on a Volkswagen abandoned on a busy boulevard in the town of Chilapa de Alvarez.

"In Chilapa selling crystal, kidnapping, extortion and stealing are strictly prohibited. This will happen to anyone who messes around," read the accompanying sign strung from two trees, according to a photo of the crime scene provided by the police to Reuters.

"Capital punishment is the sentence for all these crimes," said the sign.

The six victims have not been identified.

Guerrero, one of Mexico's poorest states, was the scene of the infamous abduction and presumed massacre of 43 students training to be teachers in the city of Iguala in 2014.

Widespread violence has wracked Mexico under the administration of President Andres Manuel Lopez Obrador, who took office in late 2018 pledging to pacify the country with a less confrontational approach to dealing with organized crime.

Lopez Obrador inherited a nation already reeling from a high murder rate. Since he took office, average annual homicide totals are on track to be the highest under any Mexican administration since modern records began.

He has faced criticism from his detractors for his security policy, which he termed "Hugs, not bullets."