Speaking at a news conference in Geneva, Jan Egeland -- UN humanitarian adviser on Syria -- warned all sides to protect civilians and medical facilities near "designated terrorist groups".

Egeland said some ambulances, health workers and schools had also been targeted in the opposition-held region.

Stating that the Syrian regime, Russia, the ISIL terror group and coalition forces should do more to prevent targeting public facilities, he said civilians and humanitarians were also bombed in ISIL-held Raqqa and Deir ez-Zour cities.

While the UN is delivering humanitarian aid to 7-9 million people in Syria, an estimated 420,000 Syrians are living in besieged areas, the UN official said.

Syria has been locked in a vicious civil war since 2011, when the Assad regime cracked down on pro-democracy protests with unexpected ferocity. Since then, hundreds of thousands of people have been killed in the conflict, according to the UN.