The Non-Governmental Organization Oxfam has withdrawn four of its aid workers who have been trapped by fighting between government forces and the opposition forces in Malakal.
Oxfam and other aid agency staff who were working inside the UN compound in the town had until today have been unable to leave since fighting began on Tuesday.
The organisation also reports a severe lack of humanitarian access across the country.
Oxfam plans to resume its activities in the UN base, where around 21,000 people are now living on Wednesday this week.
The immediate needs identified by the aid agency are for clean drinking water, food and medical care.
Oxfam ran a long term development programme in the town of Malakal until violence in December caused the agency to suspend its work.