Washington – Syria was cut off from the internet on Tuesday, according to US tech firms monitoring web traffic and the State Department.
"Syria is currently experiencing an internet blackout as of this afternoon," a State Department tweet said.
Umbrella Security Labs reported a "significant drop in traffic from Syria" starting around 18:45 GMT.
"On closer inspection it seems Syria has largely disappeared from the internet," said Umbrella's Dan Hubbard.
A similar picture came from Google through its Transparency Report on Web traffic and web monitoring firms Akamai and Renesys.
Telephone connections to and from Syria were also cut on Tuesday, according to web monitoring organisations and activists.
Telephones were not working, said activists, who were still able to use satellite connections on Wednesday.
Traffic between Syria and Google's servers ceased around 21:00 GMT Tuesday, US-based Umbrella Security Labs said.
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 29 November, 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.