Police have found the decapitated bodies of four men in the Mexican border city of Tijuana.

The Baja California state prosecutor's office says police found three of the bodies inside a home early Tuesday. An hour later, they found a fourth decapitated body inside a pickup truck.

The office said in a statement the heads were left near the bodies along with messages. It didn't say what the notes said.

Tijuana, which is across the border from San Diego, California, has faced an upsurge in drug cartel violence in recent years.

Prosecutors say 583 people have been killed so far this year in the city.