Syrian government forces and their allies drove Islamic State (IS) militants out of several villages northeast of Aleppo between Tuesday and Wednesday, a monitoring group said, bringing them closer to territory held by Turkish-backed rebels.
Advances in the last week have brought the Syrian army to within 8 km (5 miles) of the IS-held town of al-Bab, the British-based Syrian Observatory for Human Rights said.
Al-Bab, which the Turkish-backed insurgents are separately fighting to seize from the Islamist militant group, lies some 30 km northeast of Aleppo and 30 km south of the Turkish border.
Turkey said on Tuesday it would not hand over al-Bab to Syrian forces after driving out IS. The Turkish-backed rebels are closer to doing so than the Syrian army, having already reached the town's outskirts.
Observatory director Rami Abdulrahman described renewed assaults by the Syrian army which began last week as a race to recapture the city before the Turkish side got there.
The fight to seize al-Bab is one of several overlapping conflicts being fought in Syria.
The main struggle is between President Bashar al-Assad, backed by Iran, Russia and Shi'ite militias including Lebanese Hezbollah, against rebels that include groups backed by Turkey, Gulf monarchies and the United States.
But both those sides, and a U.S.-backed, Kurdish dominated alliance, are fighting separate campaigns against IS, which controls vast areas of eastern Syria and has made enemies of all sides involved in the war.
Turkey, which is fighting its own Kurdish insurgency, wants to drive both IS and Kurdish militantsfrom areas along its border.
In a sign of increasingly close Russian-Turkish cooperation even as they continue to back opposing sides, Moscow said last week its warplanes had joined forces with Turkish jets for the first time to target IS militants in al-Bab.