Gunmen ambushed and killed eight Iraqi soldiers as they were returning to base after a midnight shift in the west, security officials said Tuesday, a sobering reminder of Iraqi security forces' vulnerability as the U.S. military starts to leave. An army lieutenant was among those killed and another soldier was wounded in the late Monday night ambush, a military official and a policeman said. On Tuesday, Iraqi troops were searching for the gunmen in and around the town of Haditha in the western Anbar province, 140 miles (220 kilometers) northwest of Baghdad.