The United Nations Mission in Sudan (UNMIS) said the Nov. 21 campaign, which aims to immunize about 4.5 million children between 6 months and 15 years of age by next year, will begin instead in the southern Sudanese capital of Juba on Nov. 25.

Measles vaccination coverage in southern Sudan, where the 21- year old fighting impoverished the communities, is very low, leading to many avoidable child deaths.

UNMIS said local and international staff preparing for the campaign were among more than 100 UN and nongovernmental organizations (NGO) staff temporarily relocated from the Yambio area on Tuesday due to violence.

The fighting erupted on Monday between the Dinka and the Zande, who form the majority of the population in the Yambio region near the border with the Democratic Republic of the Congo, leading to the looting and burning of the UN health agency's compound.

The UNMIS, which is helping to consolidate a peace agreement in southern Sudan ending two decades of war between the Khartoum government and southern rebels, said the inter-tribal fighting had caused casualties, none of them so far from among the UN staff.

Meanwhile, authorities in the area have appealed for calm following a shootout and burning of some houses.

Governor of Western Equatoria state Patrick Zamoi said in a statement available here on Thursday that the situation is not out of hand, saying efforts are underway to contain the situation and restore confidence among the population.

"We have been persuading them, talking to them, cooling them down, that there is no need for arms at the moment. We have already signed peace and we want to stay in peace. If there is any problem we will solve it by dialogue," Zamoi said.

He said he has called an emergency meeting with elders from the communities to resolve the differences.

Sources said the pastoralist Dinka were displaced during Sudan' s 21-year civil war and settled in the region inhabited by agriculturist Zande.

Tensions have been rising between the two ethnic groups following the decision by Dinka to stay rather than go back to their area of origin in Jonglei State.