A suicide attack in the Russian Caucasus region of Dagestan has killed three police officers and wounded six more at a security checkpoint.

Another police officer is missing.

Russian authorities say a car filled with explosives blew up at the checkpoint just outside the town of Khasavyurt Thursday, leaving a large crater at the checkpoint. The car detonated after police attempted to stop it on its way into the city.

Russia blames frequent violent incidents in Dagestan on an Islamist insurgency seeking to establish a Muslim state in the region.