James Clapper told the Senate Armed Services Committee that the bombings against security and government targets in Damascus and Aleppo bear "all the earmarks of an Al-Qaeda-like attack."
He added that Syrian opposition groups may have been infiltrated by Al-Qaeda, likely without their knowledge.
He said the lack of a unified opposition group could leave a power vacuum that extremists could fill if the Syrian government falls, a potential development he called "troubling," because Syria has an extensive network of chemical weapons sites.
Clapper's comments follow a recent video message from Al-Qaeda leader Ayman al-Zawahiri in which he called on Muslims to support Syrian rebels.
Compiled from agency reports