A total of 66,000 people have been displaced by fighting along two fronts in Syria's fractured north, the United Nation's humanitarian coordination agency (OCHA) said Sunday.
"This includes nearly 40,000 people from Al-Bab city and nearby Taduf town, as well as 26,000 people from communities to the east of Al-Bab" in northern Aleppo province, OCHA said.
Turkey-backed rebels seized Al-Bab from ISIS on February 23 after several months of fighting.
OCHA said the 39,766 people displaced from the town fled north to areas controlled by other rebel forces, and that the "high contamination" of unexploded bombs and booby traps set by retreating jihadists was complicating efforts to return.
And since February 25, OCHA said, another 26,000 people fled violence east of Al-Bab, where Syrian government forces have also been waging a fierce offensive against ISIS.
Many of those people sought refuge in areas around Manbij, a town controlled by the US-backed Syrian Democratic Forces.
On Saturday, the Syrian Observatory for Human Rights monitoring group had said 30,000 people had been displaced by fighting between government forces and ISIS jihadists.
An AFP correspondent in Manbij saw dozens of families speeding towards the relative safety of the town on motorcycles and in minibuses and cars.
Since war broke out in Syria in March 2011, more than half of its population has been forced to flee their homes.
Aleppo province hosts tens of thousands of displaced Syrians, many in camps near the Turkish border.