Syrian President Bashar al-Assad's forces intensified air strikes on rebel-held areas across the country on Monday.
More than 42 civilians were reportedly killed and dozens more wounded in air strikes launched by the Syrian government in al-Atareb, a city in the northern Aleppo province.
READ MORE: Air strikes pound Aleppo as UN eyes new Syria talks
Against this backdrop of continued fighting in Aleppo and other provinces, Stephen O'Brien, the UN humanitarian chief, called on Monday for immediate "unconditional and unhindered" humanitarian access to an estimated 5.5 million Syrians in besieged or difficult-to-reach areas.
More than 280,000 people have been killed in Syria and more than half its population has been displaced since the conflict began.