These compounds are seen as the only places of safety as the civil war spreads. More than 60,000 people are now sheltering at UN bases across South Sudan. Food distributions have taken place at most, but the situation in Bor is so volatile that supplies have been unable to get through.
Rebels captured the town soon after Riek Machar, the former vice-president, began his revolt on December 15. Bor was then retaken by government forces loyal to Salva Kiir, the president, on Christmas Eve. Since then, the state capital has been threatened by armed militias drawn from Mr Machar's Nuer tribe.
Joe Contreras, a spokesman for the UN mission in South Sudan, said: "We are ready to provide protection to civilians under imminent threat of physical violence according to the mandate given to the mission."
Anyone without a weapon or a military uniform would receive this protection, he added.
Food was being handed out at camps in Juba, the capital, and elsewhere, but Contreras acknowledged that food distribution at Bor "had not got under way as of yesterday".