The plane, carrying an American U.N. worker, two Kenyan pilots and a Sudanese relief worker, was seized on Thursday by militia in Old Fangak in the volatile Western Upper Nile province.
"The plane is still being held and the U.N. and the government are negotiating the release," said Gillian Wilcox, spokeswoman for Operation Lifeline Sudan, an umbrella group of U.N. and other aid agencies working in Sudan.
Aid agencies fly daily into southern Sudan to deliver relief supplies to a region devastated by a 17-year-old civil war.
In its broadest terms, the war pits the Islamic government in Khartoum against mainly Christian and animist rebels of the Sudan People's Liberation Army (SPLA).
But the picture is complicated by inter-factional fighting, especially in oil-rich Western Upper Nile where numerous pro-government and rebel militia leaders are fighting for supremacy.
Militia leader Gabriel Tanginya is believed to be holding the hostages in retaliation for the capture of three of his commanders by rebels after they disembarked from another U.N. plane last month.
- Reuters - Thomson Reuters Foundation
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