Authorities in Michoacan state said gunmen opened fire on two police patrol vehicles responding to reports of a dead body left on a roadside.

Authorities in the town of Union near the border with Guerrero state said the unidentified gunmen fled following the attack. The victims were Guerrero state police officers.

Another body was found in the Gulf coast state of Veracruz on Saturday with its arms and legs mutilated and its head hacked off. The head was found in a plastic bag next to the body.

A message left with the body read: "This is for showing disrespect for the letter 'Z'," a common reference to the Zetas drug gang.

The body was wearing a state Public Safety department T-shirt, and assistant state prosecutor Jose Luis Peri said authorities are investigating whether the victim may be a police officer.

On Tuesday, federal police and navy personnel shot to death a top Zetas cartel suspect in the same area. The navy said suspect Braulio Arellano Dominguez was the reputed leader of the Zetas in Veracruz. The Zetas are a gang of hit men tied to the Gulf Cartel.

Also Saturday, the federal Attorney General's Office said it was bringing homicide and attempted homicide charges against four Chihuahua state police and two city police in the state's capital in connection with the shooting of an investigative agent during a confrontation earlier this month.

The agent had reportedly tried to stop a group of suspicious vehicles, when their occupants opened fire on him.