The United Nations said Sunday that it has completed the first aid airlift from Iraq to Syria, providing much-needed supplies to a difficult-to-access region of the war-torn country.

"The last UNHCR (UN refugee agency) cargo flight landed today at Qamishli airport carrying assistance urgently needed by displaced persons," the UNHCR said in a statement, referring to the location in northeast Syria.

It was the last of a 24-flight airlift by UNHCR, the UN's World Food Programme (WFP) and children's agency UNICEF, which started on December 15.

This "was the first time the UN has used Iraq as a hub to deliver relief items into Syria. Road convoys to eastern Syria have been perilous since May as the ongoing conflict hampered the UN's delivery efforts," the UNHCR said.

"The flights commenced as record snowfall and winter cold struck the Middle East, bringing new hardship to some 9.3 million vulnerable people across Syria, including an estimated 6.5 million internally displaced persons," it said.

During the airlift, the UNHCR sent almost 300 tonnes of aid to help over 50,000 people deal with a harsh winter, while WFP sent enough food to feed over 30,000 people for a month and UNICEF provided "health kits, water and sanitation equipment".

While the flights have stopped, overland aid shipments are continuing.

"Every week UNHCR continues to dispatch 250 trucks throughout Syria carrying relief aid to support some 75,000 persons," it said.

The conflict between forces loyal to Syrian President Bashar al-Assad and rebels seeking his overthrow has raged since 2011 and killed more than 126,000 people.