South Sudan is in a "spiraling humanitarian crisis," the United Nations warned Monday as top aid chiefs visited the world's newest country, where more than 1 million people have fled months of armed conflict. "People are in acute need," World Food Program (WFP) Director Ertharin Cousin said in Juba as she arrived in South Sudan for a two-day assessment. "Large-scale population displacement and disruption of markets and trade routes are creating a food-security crisis." More than 800,000 people are displaced inside South Sudan, while more than 250,000 have fled to the neighboring countries of Ethiopia, Kenya, Uganda, and Sudan, according to U.N. figures. Many had just returned to South Sudan after it won independence from Sudan in mid-2011, following the end of the 1983-2005 civil war. "It is heartbreaking to see that some of the very people who had fled the war two decades ago—people we helped to return to South Sudan after independence—are having to flee for their lives again, many back to the very same places where they lived in exile," said U.N. High Commissioner for Refugees (UNHCR) Antonio Guterres.