More than 66,000 people have been forced to flee fighting in northern Syria , ravaged in recent weeks by dual offensives on the Islamic State of Iraq and the Levant ( ISIL ) group, according to the United Nations.

The UN's humanitarian agency, OCHA, said on Sunday that tens of thousands of people have left their homes in northern Aleppo province, particularly around the former ISIL stronghold of Al Bab.

"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," OCHA said adding that nearly 40,000 people displaced from the town fled north to areas controlled by other rebel forces.

Since February 25, OCHA said, another 26,000 people fled violence further east, where Syrian government forces supported by Russian air power have also been waging a fierce offensive against ISIL.

It added that the "high contamination" of unexploded bombs and booby traps set by retreating ISIL fighters was complicating efforts to return.

Many of those fleeing the violence sought refuge in areas around Manbij, a town controlled by the US-backed Syrian Democratic Forces (SDF).

Al Jazeera's Natasha Ghoneim, reporting from Gaziantep on the Turkey-Syria border , said there was a "growing humanitarian crisis".

"The civilians we talked to mentioned some horrific details, including their money being stolen and also children being slaughtered by ISIL," she said.

"There's also the issue of return: when and if. ISIL have planted many mines in the neighbourhood and that will become a big issue if and when they are allowed to return home."

Long queues

An AFP news agency correspondent in Manbij said that long queues of families were still forming at checkpoints leading to the town on Sunday.

Pick-up trucks full of children and women wearing full black veils were being searched individually by SDF personnel before being allowed to enter.

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In Syria's northern province of Aleppo, where ISIL have faced simultaneous assaults in recent weeks, twin suicide attacks killed 15 people, the Syrian Observatory for Human Rights (SOHR) said on Sunday.

One attacker detonated a car bomb near the ISIL-held town of Deir Hafer, killing eight fighters with regime forces late on Saturday, according to SOHR.

ISIL claimed responsibility for the attack, saying it "was carried out by fighter Abu Abdullah al-Shami with an explosive-laden vehicle".

Deir Hafer lies on a key road linking Aleppo city to the ISIL-controlled town of Khafsah, which holds the main station to pump water into Aleppo, and further east to the group's de facto capital Raqqa.

Residents of Aleppo city have been without mains water for 48 days after ISIL cut the supply.

On Sunday, Russian and regime warplanes bombarded ISIL positions in support of Syrian troops, which had advanced to 9km from Khafsah, SOHR said.

They were just 6km from the pumping station, Rami Abdel Rahman, the head of SOHR, said.

In a second attack, ISIL said a fighter "detonated his suicide belt" in the rebel-held town of Azaz, also in Aleppo province.

SOHR said the suicide attack in the town "killed seven fighters and wounded several others, some of them in critical condition".

There was no immediate claim of responsibility for the attack in Azaz.