Islamic State militants battled rival insurgent groups on Wednesday north of the city of Aleppo, where officials say the Syrian army is preparing an offensive of its own backed by Iranian soldiers and Russian jets.
A rebel fighter and a group monitoring the war said Islamic State fighters took control of part of the towns of Ahras and Tel Jabin, about 12 km north of Aleppo, before being pushed back.
Gains by Islamic State north of Aleppo will threaten the supply lines of rival rebels inside the city, which is divided between insurgents and government forces.
The Syrian Observatory for Human Rights said the road used by Aleppo residents heading north to the Turkish border remained closed on Wednesday.
"Today there are fierce battles between us and Daesh in Ahras, Tel Jabin, and rural northern Aleppo," said Hassan Haj Ali, head of the Liwa Suqour al-Jabal rebel group, using another name for Islamic State.