BEIRUT - Al Qaeda fighters killed the leader of a rival Islamic brigade in a twin car bombing near Syria's northern city of Aleppo, an attack likely to further exacerbate rebel infighting in the country's brutal civil war even as government forces continued their intense shelling of opposition-held areas of the city on Sunday. The attack targeted the base of rivals, the Tawheed Brigades, and killed commander Adnan Bakkour, said Rami Abdurrahman of the Observatory. The al Qaeda linked Islamic State also killed another prominent commander of another rebel brigade, said analyst Charles Lister of the Brookings Doha Center. Lister...