MEXICO CITY – The heads of four people were found in Mexico, but the bodies have not been recovered yet, state officials said.

Three of the heads were found in the northwestern state of Sinaloa and the fourth turned up in the southern state of Guerrero.

Three of the heads were discovered Tuesday at 7:00 a.m. in front of a restaurant and a school in Palmillas, a town in Sinaloa, a spokesman for the state Attorney General’s Office told Efe.

Initial indications are that the victims were three unidentified young men, the AG’s office spokesman said.

The killers only left behind the heads, shocking the town, a Palmillas police department spokesman told Efe.

“Everything was quiet here. Lately, we’ve seen these kinds of things,” the police spokesman said.

A message, whose contents have not been disclosed, was left with the heads, indicating that the killings were likely linked to Mexico’s drug cartels.

Police in Ciudad Altamirano, a city in Guerrero, said a human head was found inside a cooler on Lazaro Cardenas boulevard, which links the city with Coyuca de Catalan.

The head belonged to “a person of the masculine gender, with a dark complexion, whose hair was shaved off and his facial skin removed, and a piece of cardboard with a message was left,” the Guerrero Public Safety Secretariat said.

The body has not yet been recovered and authorities have not released the contents of the message.

The head of Cesareo Pineda, police chief in the town of Petatlan, was found on Sunday, a day after he was kidnapped.

The police chief’s head was left inside a plastic cooler in front of the house of former Petatlan mayor and Regional Ranchers Union of Guerrero State, or UGREG, leader Rogaciano Alva.

Alva is wanted for the killings of 17 ranchers in clashes in the towns of Iguala and Petatlan in 2008.

Mexico has been plagued in recent years by drug-related violence blamed on powerful cartels that are battling for turf and control of the smuggling routes into the United States.

Mexico’s most powerful drug trafficking organizations, according to experts, are the Sinaloa, Tijuana, Gulf, Juarez and Beltran Leyva cartels, and La Familia Michoacana.

Los Zetas, a group of army special forces veterans and deserters who initially worked as hitmen for the Gulf cartel, may now be operating as a cartel, some experts say.

Last year, according to the El Universal newspaper, was the deadliest in Mexico in the past decade, with 7,724 people killed in violent incidents attributed to organized crime groups.

So far this year, drug-related violence has claimed the lives of more than 1,100 people, the daily says.

A total of 767 people died in drug-related violence in Sinaloa last year, while 638 people were murdered in Guerrero, the Reforma newspaper reported.

Sinaloa, located in northwestern Mexico, is the birthplace of many of Mexico’s drug lords.

The state is currently the scene of a bloody turf war between Joaquin “El Chapo” (Shorty) Guzman and the Beltran Leyva cartel, whose leaders broke off from his Sinaloa cartel.

The Sinaloa organization, sometimes referred to by officials as the Pacific cartel, is the oldest drug cartel in Mexico and Guzman, considered extremely violent, is one of the most-wanted criminals in Mexico and the United States, where the Drug Enforcement Administration has offered a reward of $5 million for him.

President Felipe Calderon, who took office in December 2006, has deployed 50,000 soldiers and 20,000 federal police nationwide to combat drug cartels and other criminal organizations.

The anti-drug operation, however, has failed to put a dent in the violence due, according to experts, to drug cartels’ ability to buy off the police and even high-ranking officials. EFE