MOGADISHU, Somalia ? At least 12 civilians were killed Monday in a suicide attack targeting African Union troops in Somalia's Lower Shabelle region, the first serious assault by suspected Islamic extremists after the killing of al-Shabab's top leader in a U.S. airstrike last week, the police and a regional official said. The attack happened near the Elasha Biyaha settlement, said Abdiqadir Mohamed Nor, the governor of Lower Shabelle. A suicide bomber detonated his explosives-laden car next to a convoy of African Union forces moving near two minibuses, said Somali police official Hassan Ali. Then, amid the...