BEIRUT — A senior U.N. humanitarian official urged Thursday for an immediate pause to the fighting around Syria’s contested city of Aleppo as government forces pounded opposition areas with airstrikes and rebels kept up their attempts to break a government siege.

In Geneva, Jan Egeland, adviser to U.N.’s special envoy to Syria, said the world body was ready to send relief to the city divided between government-controlled and opposition-controlled areas once the fighting pauses. The last delivery to reach those trapped in rebel-held parts of Aleppo – where the U.N. estimates some 300,000 residents remain – was in June, he said.

Russia had declared it is offering humanitarian corridors for residents in the area, but rights groups said such passages are not neutral and don’t offer guarantees to civilians wishing to use them.

The Britain-based Syrian Observatory for Human Rights reported at least 40 airstrikes on opposition areas of Aleppo and nearby towns.