The top U.N. peacekeeping official warned of difficult challenges in solving the conflict between the government and opposition in South Sudan, as humanitarian officials reported that they have been able to aid only one-third of the nearly 900,000 people displaced by the fighting. "It is going to be a very long, complex process to address all the deep roots of this very big crisis," Undersecretary-General for Peacekeeping Operations Herve Ladsous told reporters Tuesday after briefing the U.N. Security Council on the crisis, including efforts by the Intergovernmental Authority on Development (IGAD), a regional East African body that is mediating peace talks in Addis Ababa, where the two sides signed a cease-fire deal last month. "But, of course, it is important that the entire international community express total support for IGAD because it is the only diplomatic initiative," the U.N. peacekeeping chief said. Ladsous said the U.N. Mission in South Sudan (UNMISS) was focused on four tasks: protection of civilians, safeguarding human rights, supporting humanitarian groups, and supporting the IGAD mediation process. Thousands of people are believed to have been killed and about 870,000 others have fled their homes—145,000 of them to neighboring countries and 75,000 to U.N. bases within South Sudan—since fighting erupted in mid-December between the forces of President Salva Kiir and his former deputy, Riek Machar. The cease-fire led to a relative lull, but the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) warned Tuesday that even before the violence, the humanitarian situation was critical.