Police on Thursday found a human head inside a plastic bag dumped outside the main entrance of City Hall in this Pacific resort, a day after authorities discovered a decapitated body.

It was the fourth head found this year in Acapulco, where drug gangs have been battling each other and police for control of the local market and the resort's strategic location for smuggling drugs up the coast and into the United States.

Attached to the bag found Thursday was a note that read, "Lazcano, so that you keep sending me more idiots from GAFE," the Spanish acronym for the Special Forces Unit of the Mexican Army, which investigates drug trafficking, said police investigator Guillermo Rios Ramirez.

CountryWatch: Mexico

Lazcano is a surname and police were investigating for whom the note was intended.

The note was signed with the letter "Z," which authorities said was an attempt to link the killing to "Las Zetas," a group of former elite Mexican soldiers who now work for the Gulf drug cartel.

Authorities were investigating whether the head belonged to a decapitated body found Wednesday with the letter "Z" carved into the chest. The feet and hands were bound and the body appeared to have been dragged by a car down one of the city's main avenues.

The body was found outside the home of city employee Maria Teresa Ascencio Villasenor, a close ally of Mayor Felix Salgado. Ascencio and four of her relatives were injured May 10 when assailants launched a grenade near her home.

Neither the head nor body have been identified.

Salgado called the action of leaving the head "an act of provocation" aimed at forcing him out of the office he has held for only eight months.

Earlier this month, a severed human head washed up on the beach in the heart of Acapulco's tourist zone; the man's identity and how he was killed have not yet been determined.

In April, suspected drug hit men in Acapulco decapitated two police officers who had participated in a shootout with traffickers and left the severed heads at the scene with a note saying: "So that you learn some respect."