Beirut (AFP) - The Islamic State group is banning private internet access in its Syrian bastion Raqa, forcing residents and even its own fighters to use internet cafes where they can be monitored, activists say.

The Syrian Observatory for Human Rights and activist group Raqa is Being Slaughtered Silently both reported the new restrictions on internet access.

The activist group posted online a picture of a leaflet being distributed in the city warning internet providers they had four days to cut private wifi connections.

"The following is obligatory on all internet providers: the removal of wifi connections distributed outside of internet cafes and private connections, including for Islamic State soldiers."

The document says providers have four days from Sunday to comply with the order.

The activist group said the ban was intended to ensure "access through internet cafes only in order to monitor access."

The ban will affect not only activist groups like Raqa is Being Slaughtered Silently, which documents IS abuses in the city, but also potential defectors from within the group, the Observatory said.

"This step is part of the organisation's attempt to impose a news blackout on what is going on inside Raqa city," the Britain-based group said.

"It has been conducting patrols and raids on internet cafes, searching them for people who are transmitting news."

IS is also "trying to cut communications between its non-Syrian fighters and their families for fear of them trying to return home," it added.

Raqa, in the Euphrates Valley northeast of Damascus, is the de facto Syrian capital of the Islamic State group, which controls large swathes of Syria and neighbouring Iraq, where it rules with an iron fist.

The internet has been a rare lifeline for activists in the city, and a way for them to document life under jihadist rule.