Authorities in Mexico found the decapitated bodies of four men and a woman in Acapulco on Saturday, the latest in a string of slayings in the popular Pacific resort this week.

Federal police said the corpses of two men and a woman were found tied up in the back of a sport utility vehicle near Acapulco beach, in what appeared to be a crime related to drug gangs.

Reforma newspaper said messages were left in the vehicle linking the killings to the powerful Sinaloa cartel, headed by Mexico's most wanted capo, Joaquin Shorty Guzman.

The dismembered and decapitated bodies of two other men were found at the entrance to an outlet of Sam's Club, a unit of U.S. retailer Wal-Mart Stores Inc.

Daily Excelsior described the past few days as a black week for Acapulco, noting at least 25 people had been killed before Saturday's events.

Robberies and assaults have also plagued the port city, prompting local gas station attendants to stage a temporary walkout on Friday to protest the lack of security.

About 42,000 people have died in drug-related killings in Mexico since President Felipe Calderon went to war on the cartels shortly after taking office at the end of 2006.

Violence was long concentrated in northern Mexico, but cities farther south, including Acapulco, have increasingly been swept up in the lawlessness.