The United Nations and the International Red Cross have been forced to suspend aid operations in Syria following a fatal attack on a convoy of humanitarian supplies on Monday evening. Eighteen of the 31 trucks in the UN and Syrian Arab Red Crescent convoy were hit by what appeared to be an airstrike as the weeklong cease-fire was declared over by President Bashar al-Assad’s government. Russia denied that it or the Syrian government forces that it backs were responsible for the strike. Officials from the U.S. and UN said that they were “disgusted” and “outraged” by the attack. Twenty people in the convoy were killed, the Syrian Observatory for Human Rights reported. “At the moment [the] aid operation remains suspended while we assess and reevaluate the situation on the ground,” said a UN spokesman. A top Red Cross official said the group was “reassessing security” in the area; one of its directors in Syria was among those killed in the attack. The relief convoy was delivering medical and food aid to 78,000 people in rural Aleppo province.