An aid convoy carrying life-saving aid to 78,000 people was attacked near the Syrian city of Aleppo Monday, according to the United Nations.

The attack on the convoy, made up of Syrian Red Crescent trucks carrying UN-supplied food, was reported to have killed at least 12 people and destroyed 18 trucks laden with food intended for tens of thousands of people cut off by the war in a rural area west of Aleppo city.

Aid officials said it was hit from the air while unloading food at a warehouse in opposition controlled Urem al-Kubra. Early reports suggested most of the dead were Syrian Red Crescent drivers.

Humanitarian chief Stephen O’Brien said in a statement late Monday that a Red Crescent warehouse was also hit and a Red Crescent health clinic was reportedly severely damaged.

O’Brien said he is “disgusted and horrified” by “these sickening attacks” which he condemned in the strongest terms.

The UN Special Envoy for Syria, Staffan de Mistura, has strongly condemned the attack on the convoy, which was “the outcome of a long process of permission and preparations to assist isolated civilians.”

“Our outrage at this attack is enormous,” de Mistura said in a statement emailed to Reuters by his spokesman in Geneva.