Iraqi officials say gunmen have killed six Iraqi policemen in separate attacks in the country's west and in the capital, Baghdad. Authorities say gunmen killed five officers early on Sunday in a drive-by shooting on a police checkpoint near the desert town of Rutba. The attack in Anbar province happened on a main highway that links Iraq to Syria and Jordan. Sunni-dominated Anbar was a scene of frequent attacks by al-Qaida militants until 2008, when local Sunni tribes turned against the group and allied with U.S. forces to improve security in the province. In a second incident yesterday, authorities say gunmen killed a policeman in southwestern Baghdad. In other violence, a roadside bomb blast killed one civilian and wounded another near the northern city of Kirkuk.