An entire 20-man police force resigned in a northern Mexican town after a series of attacks that killed the police chief and five officers over the last three months.

The officers' resignation left the 13,000 people of Ascension without local police services, Chihuahua state chief prosecutor Carlos Manuel Salas said. State and federal police have moved in to take over police work, he said.

The mass resignation appeared to be connected to a Tuesday attack by gunmen that killed three of the town's officers, Salas said.

The town's police force was relatively new.