The Islamic State of Iraq and the Levant (ISIL) group has banned private internet access in its Syrian stronghold of al-Raqqa province, forcing residents and even its own fighters to use internet cafes where they can be monitored, activists say.

The Syrian Observatory for Human Rights, a UK-based monitoring group, and the activist group Raqqa is Being Slaughtered Silently both reported the new restrictions on internet access on Monday.

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 wi-fi connections.

"The following is obligatory on all internet providers: The removal of Wi-Fi connections distributed outside of internet cafes and private connections, including for Islamic State [ISIL] soldiers."

The leaflet 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".

'News blackout'

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

"This step is part of the organisation's attempt to impose a news blackout on what is going on inside Raqqa city," the AFP news agency quoted the group as saying.

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

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

Raqqa, in the Euphrates Valley in the north of the country, is the de facto Syrian capital of ISIL, 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 ISIL rule.