BAGHDAD — The lone Syrian rebel group with an explicit stamp of approval from Al Qaeda has become one of the uprising’s most effective fighting forces, posing a stark challenge to the United States and other countries that want to support the rebels but not Islamic extremists.

http://www.nytimes.com/2012/12/09/world/middleeast/syrian-rebels-tied-to-al-qaeda-play-key-role-in-war.html?pagewanted=all&_r=1&