Last night’s attack on a UN/Syrian Arab Red Crescent aid convoy, intended for 78,000 people in Aleppo, is a flagrant violation of the most fundamental principles of international humanitarian law, Amnesty International said.

Witnesses in Syria have told the organization that the convoy, along with the Syrian Arab Red Crescent warehouse where it had docked, were bombed intensively for two hours on Monday evening, heightening the suspicion that Syrian government forces deliberately targeted the relief operation.

“A sustained attack on a humanitarian convoy and workers, horrific enough in any circumstances, will in this case also have a disastrous impact not only on those desperate civilians for whom the assistance was intended, but for life-saving humanitarian operations throughout Syria,” said Philip Luther, Research and Advocacy Director for the Middle East and North Africa at Amnesty International.

“If the convoy was – as it appears – deliberately attacked, this would be yet another war crime committed by the Syrian government. It illustrates how civilians in Syria are paying with their lives for five years of total impunity for systematic war crimes and crimes against humanity. Until the international community shows that it is serious about bringing perpetrators to justice, these appalling crimes will continue on a daily basis.”

The UN aid chief, Stephen O’Brien, earlier said that the convoy was travelling with all the necessary permits, and that all parties in the conflict had been notified of its route. The UN has announced a temporary suspension of all aid convoys in Syria following the attack. Around 20 civilians were killed in the attack, according to the International Committee of the Red Cross.

Witnesses interviewed by Amnesty International said a variety of aircraft, including helicopters and Russian-made fighter jets, took part in the bombardment, in the town of Urum al-Kubra in the west of Aleppo governorate. Twenty-one of the 31 trucks in the convoy had been partially or completely destroyed.

“The explosions focused only on the vicinity of the Red Crescent center, which is far from any military presence. I couldn’t initiate a search and rescue operation until the bombing stopped… it kept going for at least two hours,” a rescue worker in Urum al-Kubra told Amnesty International.

Abu Haytham, a media activist, said he heard a warplane in the area but had never imagined that the Syrian Red Crescent building would be targeted. When he arrived at the site after the bombardment, many trucks were aflame and the building had been destroyed.

“I saw the bodies of men on the ground,” he said. “I was told they were truck drivers and volunteers who had been unloading the trucks. The trucks had the logo of UNHCR. The aid included medicine, food and other desperately needed items.”