Egypt has cut off nearly all Internet traffic into and out of the country in the largest blackout of its kind, according to firms that monitor international data flows.

Cellphone networks were also disrupted. Vodafone said in a statement on its Web site that “all mobile operators in Egypt have been instructed to suspend services in selected areas.” The company said it was “obliged to comply” with the order.

Egypt has been trying to contain growing protests that have been fueled in part by videos and other information shared over social networks like Facebook and Twitter.

Renesys, a Vermont-based company that tracks Internet traffic, said that just after midnight Cairo time, or 5 p.m. New York time, Egyptian authorities had succeeded in shutting down the country’s international access points.