The United Nations has suspended all aid shipments to Syria after at least 20 people were killed in an airstrike on a relief convoy and a warehouse near the Syrian town of Urum al-Kubra on Monday, BBC reported. The attack on the UN and Red Crescent convoy came hours after Syria withdrew its support for the ceasefire agreement on the civil war in the country brokered by the United States and Russia. Omar Barakat, the director of a Syrian Arab Red Crescent branch, was among the victims, CNN reported.

Moscow has blamed rebel forces for the attack, but officials have not confirmed the allegations. The Syrian army has denied its forces' involvement in the incident. The US and Russia are scheduled to discuss the situation in New York. The agreement was threatened when US-led coalition planes struck Syrian army personnel in Deir al-Zour on Sunday, in what Washington claims was an "unintended mistake"

UN aid chief Stephen O'Brien said that if the attack was deliberate it would amount to war crime, BBC reported. The UN has said that at least 18 of the 31 lorries in the convoy were hit near the rebel-held town. Washington said it would study the situation to decide on continuing cooperation efforts with Russia.

Moscow and Washington on September 10 announced a ceasefire plan for the “cessation of hostilities” between the Syrian government and opposition militia in the war-torn country. The civil war in the West Asian country began in 2011 following massive protests against the Assad regime. The Syrian government has been accused of committing atrocities against civilians such as dropping barrel bombs in populated areas as well as using chemical weapons. While Washington has supported rebel groups, Moscow is seen as a an ally of the Syrian president.