Severe winter weather delayed the start of the first United Nations airlift of aid items from Iraq's autonomous Kurdistan region to neighbouring Syria, a spokesman said.

"It appears... the weather in Qamishli has delayed the start of the airlift, as well as prevailing conditions across the region," UN refugee agency (UNHCR) regional spokesman Peter Kessler said on Thursday, referring to the city in northeast Syria to which aid supplies are to be flown.

"When it will start is difficult to say -- I think the authorities in Qamishli are going to check conditions at the airfield on Friday; they announced yesterday a 48-hour delay," he said.

The airlift, which has been given the go-ahead by both the Syrian and Iraqi governments, was initially expected to begin on Thursday.

UNHCR plans to fly some 40 metric tonnes of aid into the area, which has become increasingly dangerous to reach, providing "core relief items for 10,000 families, or about 50-60,000 people," Kessler said this week.

The UN's World Food Program and children's agency UNICEF were also to send aid into Syria via air.

UNHCR plans to spend $US195 million ($A216.19 million) to help "winterise" Syria and the surrounding countries.

As part of the program, the agency has already begun distributing things like isolation tents, plastic sheeting, warm clothing, especially for children and other vulnerable people, and cash for fuel.

The civil war between forces loyal to Syrian President Bashar al-Assad and rebels seeking his overthrow has raged for 33 months and killed more than 125,000 people.