UNITED NATIONS - The UN Refugee Agency (UNHCR) on Tuesday launched a massive airlift operation from Kenya to South Sudan to bring aid to around 50,000 Sudanese refugees, UN spokesman Martin Nesirky told reporters here.

"The first of 18 scheduled arrived on Tuesday morning, carrying 12 tons of supplies, including plastic sheets and rolls, sleeping mats, blankets, mosquito nets, buckets, jerry cans and kitchen sets," Nesirky said at a daily news briefing.

The items will be distributed to refugees in Upper Nile state, close to sites where the refugees have settled, and Unity state which have been hosting refugees fleeing the fighting in Sudan's Blue Nile and Southern Kordofan states, he said.

According to the Refugee Agency, at least 40,000 refugees have arrived in Upper Nile state since September and 22,000 refugees from the Nuba mountains of Southern Kordofan have fled to Unity state since August.

The remaining 17 flights will deliver an additional 272 tons of relief supplies from UNHCR's stockpiles in Nairobi to Malakal. The stocks will then be taken by road either to Maban county in Upper Nile, some 300 kilometers to the north-east, or westwards to Unity state. The airlift will cost an estimated $1.5 million, while the aid supplies being delivered are valued at 2.5 million dollars.

In addition to airlifts, UNHCR plans to send 10,000 tents to South Sudan from a warehouse in Dubai in the coming weeks at an expected cost of more than 8 million dollars.

Upper Nile and Unity states in South Sudan have been receiving refugees from fighting in Sudan's Blue Nile and Southern Kordofan states in recent months.