Police found the bodies of seven people Wednesday at an athletic facility in the northern Mexican town of El Pino, sources in the Durango state Attorney General's Office told Efe.

The victims were naked and covered with bruises, but the officers at the scene did not notice any bullet wounds on the bodies.

The one woman and six men - ranging in age from 16 to 75 - were all reported missing on Monday and have been positively identified by their families, the sources in the AG's office said.

They said a message was left with the bodies, but declined to reveal its content.

Such messages are often a feature of killings by drug cartels and other organized-crime elements.

Mexican soldiers found some 200 bodies earlier this year in mass graves in Durango, a state where the Sinaloa cartel and the remnants of the Beltran Leyva gang are battling for control of the trade in illegal drugs.

Durango and the neighboring states of Chihuahua and Sinaloa make up Mexico's "golden triangle" of marijuana and opium-poppy plantations.

The fugitive head of the Sinaloa cartel, billionaire Joaquin "El Chapo" Guzman, is rumored to be hiding out in Durango.