Authorities found five decapitated bodies in western Mexico, with letters left with the corpses purportedly signed by a drug cartel, officials said.

The bodies, with their heads laying nearby, were found shortly before dawn on Saturday, in two different locations in Michoacan state, a region struggling with gang turf wars.

Three headless corpses were found on a bridge's traffic circle in Tarimbaro, a suburb of Morelia, the state's capital, said Michoacan chief prosecutor Marco Vinicio Aguilera.

"A knife that may have been used to cut the heads was found in the area," he told AFP.

Around an hour later, two more were found in a Morelia public square, with the heads on a sidewalk a little further away, Aguilera said.

A letter signed with the initials of the Jalisco New Generation drug cartel were found with all the bodies.

The gang, which operates in the neighboring state of Jalisco, is engaged in a heated turf battle with the Knights Templar cartel, which has dominated Michoacan's drug trade in recent years.

The extortion and murders committed by the Knights Templar prompted several towns to form vigilante militias in February.

Authorities say some of the self-styled "self-defense" units are supported by the Jalisco drug cartel, a charge the vigilantes deny.

The federal government deployed thousands of troops to Michoacan in May to crack down on the cartels, but gruesome acts of violence have continued.

Just last week, three local police officers were assassinated in the span of two days.