A group linked to al Qaeda recaptured much of its stronghold in the northeast Syrian city of Raqqa on Sunday, activists said, dealing a blow to rival rebel groups backed by Gulf Arab and Western states.

In the province of Aleppo west of Raqqa, activists said ISIL had regained several rural towns, including Hrietan and Basraton, where ISIL killed a senior commander in the Nour al-Din Zanki brigades, a key unit in the newly-formed Mujahideen Army, which has been fighting ISIL in Aleppo.

Fighting also raged on Sunday between Western-backed Free Syrian Army units around the town of Renayan near Aleppo and in Urum to the east, as rebel infighting made the city vulnerable to advances by Assad's forces, the sources said.

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