Islamic State militants raided Internet cafes in their Syrian stronghold city of Raqqa after ordering a ban on wireless networks that can be used by private homes, the Syrian Observatory for Human Rights monitoring group said Monday.

In order to implement a news blackout of the group's activities, IS had given cafe owners four days from Sunday to disconnect wireless Internet networks used by residents, the Observatory said, citing an IS leaflet circulated in Raqqa.

The United States said earlier this month it had intensified an aerial campaign against IS in Syria with a wave of strikes in and around Raqqa, de facto capital of the militants' self-declared caliphate in parts of Syria and Iraq.