The attackers ambushed a police mobile vehicle on Munir Mengal Road and fled.
Police said that two policemen were killed on the spot and two were injured who were rushed to a hospital.
"Later one of the injured men died while other is stable," police said.
Pakistani Taliban militants have claimed responsibility for the attack which comes after the deadly assault on the Bacha Khan University in Khyber-Pakhtunkhwa on January 20 that killed at least 21 people. Balochistan has faced persistent separatist and ethnic violence.