UNITED NATIONS (Reuters) - The United Nations carried out its first airdrop of humanitarian aid to the Syrian city of Deir al-Zor on Wednesday, U.N. aid chief Stephen O’Brien said, delivering 21 tons of relief to civilians besieged by Islamic State militants.

“Earlier this morning a WFP (World Food Programme) plane dropped the first cargo of 21 (metric) tons of items into Deir al-Zor,” O’Brien told the U.N. Security Council. “We have received initial reports ... that pallets have landed in the target area.”

However, U.N. spokesman Stephane Dujarric later told reporters the WFP was still trying to get information on where the aid ended up, suggesting 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 trying to reach local partners to ensure that the aid was received.

“There may have been some difficulties in terms of the pallets,” he added.

Dujarric said there would likely be further airdrops in the coming days.

The WFP said in a statement to Reuters that “the operation faced technical difficulties and we are debriefing crew and partners in Deir (al-Zor) to make necessary adjustments.”

“The team will try again when possible to deliver assistance to up to 200,000 people in desperate need in the besieged city whom we have not been able to reach since March 2014,” it said. “High altitude drops are extremely challenging to carry out and take more than one trial to develop full accuracy.”