Internet and telephone connections to and from Syria were cut Tuesday, according to web monitoring organizations and activists, dpa reported.
Telephones were also not working, said activists, who were still able to use satellite connections Wednesday.
Traffic between Syria and Google's servers ceased around 2100 GMT Tuesday, US-based Umbrella Security Labs said.
"It seems Syria has largely disappeared from the internet," the company wrote on its Global Transparency blog on Tuesday.
The government was previously believed to have cut internet access on a regional basis in advance of major battles, to disrupt rebel communications and prevent reports reaching the outside world.
The last nationwide internet outage lasted nearly three days from November 29, according to Umbrella Security.
The latest disruption comes days after an Israeli airstrike and amid allegations that both the regime and rebels have used chemical weapons.