NAIROBI, Kenya (AP) _ United Nations officials are negotiating for the release of 22 employees taken from a food barge by rebels in southern Sudan, the head of the U.N.'s Sudan relief efforts said Tuesday.

Two foreigners were among those seized, Mirko Rizzuto, 29, of Italy, and Romy Delos Santos, 57, of the Philippines. Both work for the U.N.'s World Food Program.

Phillip O'Brien, head of the U.N.'s Operation Lifeline Sudan in Nairobi, said the rebels fired on the barge Sunday, forcing it to shore on the White Nile River west of Malakal in Upper Nile province.

Rizzutto was seized at that point, O'Brien said, and the barge was allowed to continue.

But it was intercepted again by another band of rebels, O'Brien said, and forced to sail to the village of Tonga, about 60 miles west of Malakal where the 21 other employees are being held.

O'Brien said the United Nations sent a plane to Tonga on Tuesday and hoped to have word soon on the release of the prisoners. He said they had been in radio contact and were ``well and safe.''

In addition to the two foreigners, the captives included the Sudanese barge crew of 13 and seven Sudanese employees of the World Food Program and the U.N. Children's Fund.

O'Brien said the rebels claimed they had not been notified of the food deliveries, although he said ranking commanders had been told well in advance.

The barge started off with 785 tons of relief supplies destined for 185,000 people in 20 towns along the river, said Sylvana Foa, spokeswoman for the World Food Program in Rome.

Operation Lifeline Sudan, an umbrella organization for aid agencies, was established in 1989 to feed hundreds of thousands of southern Sudanese displaced by civil war.

It delivers emergency supplies by plane, truck and barge. Barges and truck convoys have frequently been stopped and looted over the years.

At U.N. headquarters in New York, Peter Hansen, the head of relief operations, demanded the release of the abducted workers and warned that failure to respect the safety of relief workers ``can only result in greater suffering for those affected by emergencies.''