The mutilated remains of 18 people, including some who were beheaded, have been found close to a highway near the western Mexican city of Guadalajara, officials say.
Heads and other body parts have been found inside two four-wheel drives abandoned at kilometre 25 of the Guadalajara-Chapala highway in the city of Ixtlahuacan de los Membrillos, Jalisco state attorney-general Tomas Coronado Olmos says.
Olmos says he met Governor Emilio Gonzalez Marquez and Public Safety Secretary Luis Carlos Najera to discuss the situation and take measures to prevent more killings.
Police found the bodies near the Edy Motel, just off the highway that links Guadalajara, the capital of Jalisco, to Chapala.
The vehicles were parked near the Burritos de Moyahua restaurant in an area known as La Querencia.
Officers went to the scene after receiving an anonymous telephone call around 7.48am (2248 AEST) on Wednesday from a woman who spotted the bodies.
The identities and genders of the victims have not been determined, officials say.
Jalisco state medical examiner's office personnel removed the human remains from the vehicles.
A total of 18 heads were found in the 4WDs and are being analysed by specialists, the medical examiner's office has told the AG's office.
The medical examiner's office plans to conduct DNA and other tests on the remains in response to a request from the AG's office.
A message from the Los Zetas drug cartel threatening the leaders of the rival Sinaloa cartel was found in one of the 4WDs, Ixtlahuacan de los Membrillos police department spokesmen say.
The Zetas, a band of special forces deserters turned outlaws, have been locked in a turf war in Jalisco with Joaquin "El Chapo" (Shorty) Guzman's Sinaloa drug cartel, which operates in the state via an ally, the Jalisco Nueva Generacion gang.
The bodies of 26 people were discovered on November 24 inside three vehicles abandoned on a main thoroughfare in Guadalajara, Mexico's second-largest city.
Authorities later blamed that slaughter on Los Zetas.
The cartels have stepped up their war in recent weeks, engaging in a number of shootouts, including one in Nuevo Laredo, a border city in the northeastern state of Tamaulipas, that left 23 members of both criminal organisations dead.
About 50,000 people have died in Mexico's drug war since December 2006, when President Felipe Calderon declared war on the country's powerful cartels, sending soldiers into the streets to fight criminals.
