Syria's Internet shutdown is unprecedented in the conflict, though Damascus has partially cut off access several times over the past 20 months.
Activists in Syria reached Thursday by satellite telephone confirmed the unprecedented blackout, which comes amid intense fighting in the capital, Damascus.
Renesys, a US-based network security firm that studies Internet disruptions, says Syria effectively disappeared from the Internet at 12:26 p.m. local time.
Akamai Technologies Inc., another US-based company that distributes content on the Internet, also confirmed a complete outage for Syria.
Syria has partially cut Internet connections during the 20-month uprising against President Bashar Assad but a nationwide shutdown is unprecedented.