Assailants opened fire on a car, killing four Shi'ite Muslims hours before a member of the rival Sunni sect was shot dead in northwestern Pakistan on Monday in apparent sectarian violence in which a policeman also died, police said. The officer died in a shootout while pursuing the car's attackers Dera Ismail Khan, area police chief Silahuddin Khan said. He said the attackers were riding on a motorcycle, and the slain men included two brothers and two of their friends. "It seems to be a sectarian attack, but we are still investigating," Khan said. He said the victims were in conflict with an outlawed Sunni militant group accused of targeting Shi'ite Muslims across the country. Hours later, an attacker wearing a mask and riding on a motorcycle shot and killed a Sunni Muslim member of Dera Ismail Khan city council, and wounded two of his friends, Khan said. Although most Sunni and Shi'ite Muslims live together peacefully, extremists on both sides often target the other's leaders and activists. The majority of Pakistan's Muslims are Sunni.