"The most dominant of the extremist groups is Jabhat al-Nusra. The U.S. has declared it a terrorist organization, claiming it has ties to al-Qaida.

The group claimed responsibility Monday for a suicide car bombing that reportedly killed dozens of Assad's loyalists last week.

In a statement posted online, it said one of its suicide bombers detonated a car bomb Jan. 21 at the headquarters of a pro-government militia in the central province of Hama. It said the bomber drove a truck packed with explosives to the militia's complex in the town of Salamiya and blew himself up "to give the tyrannical regime a taste" of violence it has been inflicting on the Syrian people.

Activists said at least 42 people, mostly pro-Assad militiamen, were killed in the blast. The government did not say how many people were killed, although two days after the bombing, state-run SANA news agency published photographs of what it said was a funeral procession for the blast's victims. In one of the photographs, a dozen men are seen standing behind 11 caskets, wrapped into a Syrian flag."

That black flag with the Shahada (profession of faith) in white has been adopted by most Al Qaeda associated groups, except the North African AQIM, which uses black on white.