Syrian opposition activists say the Islamic State group has captured several villages in the northern province of Aleppo during clashes with government forces.

The Britain-based Syrian Observatory for Human Rights says the fighting is concentrated in areas east of the town of Khanaser, which has exchanged hands several times in recent months.

An activist based in Aleppo says IS launched its latest offensive in the area a day earlier and by Saturday was in control of some 18 small villages.

The activist spoke on condition of anonymity for fear of reprisals from IS.

Khanaser is strategic since it's on the highway that links government-held parts of Aleppo with the rest of the country.