The United Nations carried out its first airdrop of humanitarian aid to the Syrian city of Deir al-Zor on Wednesday, said UN aid chief Stephen O'Brien, delivering 21 tons of relief to civilians besieged by Islamic State militants."Earlier this morning a WFP (World Food Program) plane dropped the first cargo of 21 tons of items into Deir al-Zor," O'Brien told the UN Security Council. "We have received initial reports ... that pallets have landed in the target area."However, UN spokesman Stephane Dujarric later told reporters the WFP was still trying to get information on where the aid ended up, suggesting that it may not have all reached the target area."As you know, airdrops can be very challenging," he said. "The pallets were dropped. They're (the WFP) trying to reach local partners to ensure that the aid was received."