Guadalajara (Mexico) (AFP) - A dozen bodies -- including seven that were headless and mutilated -- were discovered over the weekend in western Mexico's seaside resort of Manzanillo, apparent victims of the country's epidemic of drug violence, local officials said.

It was a shocking turn of events for an area popular with American and other foreign tourists, which until now had largely been spared from the bloody drug wars wracking other parts of Mexico.

Seven bodies were found early Saturday in an abandoned taxi on the road from Manzanillo to the town of Cihuatlan.

The bodies were "mutilated, apparently decapitated, and one of the victims was a woman," the port city's police chief Carlos Heredia told AFP.

On the vehicle was a message signed by the increasingly powerful Jalisco New Generation drug cartel, he said.

That cartel is blamed for a surge in murders in the tiny Pacific state of Colima, where Manzanillo is located.

On Sunday, five half-naked bodies were found dumped in a forested area, a municipal police commander told AFP, speaking on condition of anonymity because he was not authorized to brief reporters.

The bodies showed signs of torture and were left with two green cards signed by the Jalisco New Generation cartel, he said.

The Colima state attorney's office said in a statement it was "seeking those responsible for depriving five people of their lives, whose bodies were found Sunday afternoon" on the highway between Manzanillo and Minatitlan.

Authorities have not said if the two sets of victims were related. None have yet been identified.

The past six months have seen an increase in killings linked to disputes within the Jalisco cartel, police records showed.

On January 16 and 17, six people were shot to death in three separate incidents in Manzanillo. Authorities believe all were linked to organized crime.

With drug baron Joaquin "El Chapo" Guzman's recent extradition to the United States, his powerful Sinaloa cartel is expected to face a rising challenge from the Jalisco gang, a onetime ally now estimated to be worth $50 billion.

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The Jalisco group's incursions into Sinaloa territory have turned Colima state into the Mexican region with the highest homicide rate, with 72 killings per 100,000 inhabitants last year.

The gang, also known by its Spanish initials CJNG, has also launched bold attacks on the police and military.

In March and April 2015, the cartel killed 20 police officers in two separate ambushes in western Jalisco state. In May of that year, the gang used a rocket-propelled grenade to down a military helicopter, killing seven soldiers and a policewoman.

The latest killings in Manzanillo came less than a week after a mass shooting in another normally peaceful Mexican resort, this one on the Caribbean coast.

Gunfire erupted early Monday at a music festival in Playa del Carmen, south of Cancun, leaving at least five people dead and 15 injured, the mayor said. Three of the dead were foreigners.

Authorities attributed the attack to a turf war between drug cartels.

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