The "Islamic State of Iraq and the Levant" (ISIL) has imposed an "Afghan-style" dress code on men in its Syrian stronghold of al-Raqa to help its fighters blend into the civilian population, AFP reported Monday (March 6th).

For more than two weeks, the group has been requiring men to wear the "Afghan-style" clothing adopted by its fighters, said al-Raqa is Being Slaughtered Silently activist Abu Mohamed.

"Anyone who does not comply faces prison and fine," he said.

The new restriction comes as the Syrian Democratic Forces (SDF), an Arab-Kurd opposition alliance, approaches al-Raqa city, backed by coalition air strikes.

The rule is an attempt to make it harder for aircraft and the SDF to distinguish between civilians and ISIL fighters, Abu Mohamed said.

The Syrian Observatory for Human Rights also reported the new rule in al-Raqa.

Observatory director Rami Abdel Rahman said the rule was imposed so that "informants" giving co-ordinates to the coalition would not be able to distinguish between civilians and ISIL fighters.

Abu Mohamed described a "state of alert" in al-Raqa, with new checkpoints springing up.

The Observatory said both civilians and ISIL families were attempting to flee into al-Raqa province from neighbouring Aleppo, where ISIL is under assault.

"Thousands of families in recent days have tried to reach the administrative borders of al-Raqa province, along with around 120 families of fighters and commanders of ISIL," the Observatory said.

The SDF on Monday cut a key supply route between al-Raqa and ISIL-held territory in Deir Ezzor province to the east, and is now eight kilometres from al-Raqa to the northeast, according to the Observatory.

ISIL has been preventing civilians from entering the province "but granted families of its fighters" a document allowing "passage to al-Raqa city by boat, as ground transportation is now impossible because the bridges across the Euphrates have been destroyed", the Observatory said.