People on the ground are reporting the outage, as well. Wired's Danger Room, per one source who works with Syrian rebels, confirmed that at least some of the country's Internet access is down.
We're not sure, at this point, what (or who?) caused the outage. Internet infrastructure is notoriously fragile; a single cut cable can disrupt service to several regions -- not just countries, but regions -- at the same time. Accidents can happen, easily.