STEPHEN O’BRIEN pleaded with UN Security Council members to protect civilians for the sake of humanity.
He said failure to take a decisive action could expose Aleppo to the risk of becoming one giant graveyard.
The warning comes as Syrian government force advance on rebel-held areas.
Troops and militiamen have retaken more than a third of the rebel-held eastern part of Aleppo since the weekend.
Latest reports indicate that at least thirty-four people died in the shelling of government and opposition-controlled areas.
