Raw : The leader of congress of Mexico's southern state of Guerrero was shot dead in his car, while three human heads showed up in ice coolers elsewhere in the state, officials said Thursday.

Guerrero is home to beach resorts including Acapulco, but is also a drug trafficking hub which has seen brutal killings and beheadings linked to the country's powerful cartels in recent years.

Leftist politician Armando Chavarria Barrera was found with bullet wounds to his head and stomach in state capital Chilpancingo, a public security ministry statement said. The motive for the crime was unclear, it added.

Members of his PRD party said the killing was a political crime, and told a Mexico City news conference that 25 of the party's members had been assassinated in 2009.

Police on Thursday, meanwhile, recovered three human heads in ice coolers, and their body parts stuffed in bags, in a small town in the mountains of Guerrero, the public security ministry said.

News reports said a message criticizing the powerful La Familia drug gang also lay nearby.

Almost 10,000 people have died in suspected drug-related attacks in Mexico since the start of last year, amid a crackdown on organized crime involving more than 36,000 troops.