"A number of opposition battalions... united under the name 'Army of the Mujahideen' fought fierce battles against the Al-Qaeda-linked Islamic State of Iraq and the Levant (ISIL) around Atareb" in the province of Aleppo, said the Syrian Observatory for Human Rights.

The Britain-based Observatory also said at least four ISIL members were killed in the fighting.

Activists said a number of local rebel groups were involved in the fighting against ISIL, and distributed an amateur video apparently showing "the detention of an ISIL member who was fighting the (rebel) Free Syrian Army in Atareb."

Aleppo city-based activist Nazeer al-Khatib meanwhile reported fighting in several neighborhoods, including Sukkari, Ansari, Bustan al-Qasr and Salaheddin, pitting rebels against ISIL. Other parts of the city are held by army troops.

The fighting comes two days after ISIL reportedly tortured and assassinated a doctor, affiliated to rebel groups.

Witnesses accused ISIL militants of opening fire against the civilians.

NJF/NJF