The United States and its allies are facing what could be a major setback in efforts to influence the outcome of Syria’s civil war. A coalition of Syrian rebel groups has openly split with the Western-backed foreign opposition. In a joint statement, 13 armed rebel factions, including units of the Free Syrian Army, said they reject the authority of the Turkey-based National Coalition, which is backed by countries including the United States and Saudi Arabia. The new front has dubbed itself the “Islamist Alliance” and claims to represent three-quarters of the armed rebels fighting the Assad regime. The alliance’s lead signatory is the al-Nusra Front, an al-Qaeda-linked group deemed a terrorist organization by the United States.