Two human heads have been found in Mexican cities with threatening messages.

State police in Cuautitlan, near Mexico City, say one head turned up in a box left in the parking lot of their office.

A state police official who isn't authorized to give his name says it came with a warning that federal police and members of the drug gang La Familia will be beheaded. La Familia operates out of Michoacan state, to the west.

State prosecutors in Michoacan say another head turned up Friday in an ice chest in the port of Lazaro Cardenas. Tape covered the eyes and an attached message read: "From the Gulf Cartel."

The heads were the latest in a wave of drug-related violence in Mexico.