Hamas leader Ismail Haniyeh was killed by a predawn airstrike in the Iranian capital Wednesday, Iran and the militant group said, blaming Israel for a shock assassination that risks escalating the conflict even as the U.S. and other nations were scrambling to prevent an all-out regional war. Iran's supreme leader vowed revenge against Israel. There was no immediate comment from Israel, which has pledged to kill Haniyeh and other Hamas leaders over the group’s O