The severed heads of six state police investigators were found at a public plaza Wednesday in the northern Mexican state of Durango.

The heads were found in the township of Cuencame a day after the officers were reported kidnapped, state prosecutors' spokesman Ruben Lopez said.

There was no information on the possible motive for the slayings, but beheadings are a hallmark of Mexico's brutal drug gang violence. Durango, a mountainous, largely rural state, is a major battleground for drug trafficking territory.

In Tijuana, meanwhile, the bodies of three young men were found in one neighborhood. A fourth body was found outside a hospital, and a fifth — whose hands and feet were bound — was found dumped near a gas station.

The deaths came a day after 12 bodies were found in Tijuana, including four that had been decapitated and four men killed in a shootout at a popular seafood restaurant.

Tijuana, across the border from San Diego, has seen over 590 deaths in violence apparently related to drug disputes this year.

Nationwide, more than 14,000 people have died in drug gang violence since President Felipe Calderon sent troops and federal police to fight cartels three years ago.

In Calderon's home state of Michoacan, federal police arrested a leader of La Familia drug cartel suspected in several shooting and grenade attacks against police, including a Dec. 9 shooting that killed one officer.

The suspect, Antonio Chavez Andrade, also known as "the Nephew," told investigators the cartel had stepped up attacks against federal police because recent crackdowns were hurting La Familia's operational and economic capabilities, according to a statement from the federal Public Safety Secretary.