UN chief Ban Ki-moon on Friday voiced \"extreme concern\" about the conflict in South Kordofan and urged Khartoum and Juba to reach a political accord on Abyei, just hours before south Sudan proclaims independence. \"I am extremely concerned about the ongoing violence in Southern Kordofan and its impact on civilians,\" Ban told reporters in Khartoum, after meeting Sudan\'s Foreign Minister Ali Ahmed Karti. \"That is why I have again urged the Sudanese government and the Sudan People\'s Liberation Movement (North) to conclude a ceasefire as a matter of priority,\" he added, shortly before flying to Juba. Fighting erupted a month ago, between government forces and militia aligned to ex-rebel army the SPLA, in the ethnically divided northern state of South Kordofan, which the UN peacekeeping mission in Sudan (UNMIS) is due to officially start withdrawing from on Sunday, after its mandate expires. The United States said on Thursday that maintaining a UN peacekeeping presence in the embattled state was \"vital\" to peace and humanitarian efforts, despite Khartoum\'s insistence on not renewing its mandate. More than 70,000 people have fled the violence in South Kordofan, according to UN estimates, although reliable figures are nearly impossible to come by, given the heavy restrictions on UN agencies and NGOs operating there. The SPLM North says more than 700,000 people have been displaced. Ban said that UN personnel must be allowed unfettered access to civilians requiring assistance, and that he had asked the Sudanese government \"one last time\" to allow a temporary extension of the UNMIS mandate. \"We cannot afford to have any gap at this critical juncture,\" he said. The UN chief also urged future cooperation between north and south Sudan, particularly over the disputed border region of Abyei, the most intractable of the issues the two sides failed to resolve pre-partition. \"I know secession is painful, emotionally and financially... While the people of north and south Sudan will soon live in different countries, their future will be closely linked,\" Ban said. \"Ties of culture, politics and commerce compel both to face their common future as partners, not as rivals. A viable south Sudan requires a viable north Sudan.\" The UN Security Council last month ordered a 4,200-strong Ethiopian peacekeeping force into Abyei in a bid to douse tensions there ahead of southern independence. The peacekeepers will monitor the withdrawal of north Sudan troops who occupied the border region on May 21, prompting more than 100,000 ethnically southern residents to flee south. \"As we prepare to deploy Ethiopian troops in the UN Interim Security Force for Abyei, as a temporary arrangement, the parties must make the political compromises necessary to resolve this question,\" Ban said.