BAGHDAD--A U.S. airstrike killed a man suspected of directing the Aug. 14 truck bombings in northern Iraq that caused the deaths of more than 400 people, the deadliest single attack since the American-led invasion of Iraq in 2003, military officials said Sunday. The man, Abu Mohammed Afri, was a leader of Al Qaeda in Iraq, U.S. officials said, and was responsible for the synchronized bombings that targeted the Yazidi religious sect, a minority that is neither Muslim nor Christian. The bombings leveled neighborhoods of crude earthen homes and shops, burying victims and overwhelming medical facilities in Nineveh province. Hundreds of...