-LRB- CNN -RRB- -- A huge aid effort is under way in a remote area of South Sudan to help an estimated 60,000 people who fled their homes to escape roaming fighters , the United Nations said . Some 6,000 armed men from the Lou Nuer tribe marched on an area of Jonglei state , which is home to the rival Murle tribe , attacking the town of Pibor last weekend . Although the Lou Nuer fighters have left , following negotiations with U.N. peacekeepers and the South Sudan authorities , help is urgently needed for those who fled , the U.N. Mission in South Sudan -LRB- UNMISS -RRB- said Friday . The special representative for the U.N. Secretary-General in South Sudan , Hilda F. Johnson , is traveling to Pibor on Saturday to see the situation , UNMISS spokesman Kouider Zerrouk said . The South Sudan government has declared Jonglei a `` humanitarian disaster area '' and appealed for international help . Aid workers estimate that 60,000 people are in need of assistance and the U.N. World Food Programme voiced concern Friday that food shortages in the area `` could reach crisis levels . '' It has already made emergency food deliveries . U.N. Humanitarian Coordinator Lise Grande said some of the people who fled into the bush to escape the fighters are starting to return to their homes , according to a statement . U.N planes are also trying to find other families still hiding out in the bush , she said . `` But there are a number of villages that were burned completely to the ground , for example , Likuangole , and in that case people are not coming back and that 's because there is nothing to come back to , '' she said . Ethnic tensions in Jonglei state have flared as tribes fight over grazing lands and water rights , leading to cattle raids and abduction of women and children . Government officials have urged the two ethnic groups to return women and children abducted in the spate of violence . The violence in Jonglei state is the latest to rock South Sudan , which officially gained its statehood in July after separating from neighboring Sudan to the north . U.N. High Commissioner for Refugees Antonio Guterres is also in South Sudan this weekend , to see other areas affected by conflict . Among them will be a refugee site in Mabaan , where tens of thousands of refugees have sought help since fleeing fighting across the border in Sudan 's Southern Kordofan and Blue Nile States . U.N. flights have delivered thousands of tents , kitchen sets , blankets , jerry cans , plastic sheets , sleeping mats , mosquito nets and other essential items to Mabaan and another refugee camp at Malakal in the past two-and-a-half weeks . Decades of civil war between the north and south , costing as many as 2 million lives , ended with a U.S.-brokered peace treaty in 2005 . But before South Sudan gained independence in July , human rights monitors expressed concerns that long-standing grievances could end in violence consuming the region again . The United Nations estimates that more than 1,100 people died and 63,000 were displaced last year by inter-communal violence in Jonglei state , not taking into account the latest clashes . U.S. President Barack Obama gave his approval Friday for the sale of weapons and defense services to South Sudan . The decision could open the door to South Sudan acquiring air defenses . It has accused Sudan of carrying out aerial bombardments on its territory . The White House condemned air raids by the Sudan Armed Forces on South Sudan in November , saying : `` These provocative aerial bombardments greatly increase the potential for direct confrontation between Sudan and South Sudan . The memorandum sent by Obama Friday to U.S. Secretary of State Hillary Clinton said the `` furnishing of defense articles and defense services to the Republic of South Sudan will strengthen the security of the United States and promote world peace . '' CNN 's Laura Smith-Spark and Pierre Meilhan contributed to this report .