Juba - Millions of South Sudanese made homeless, hungry or both from a fresh eruption of violence are in desperate need of more assistance, the United Nation's humanitarian chief has said.Stephen O'Brien, head of the UN Office for the Coordination of Humanitarian Affairs, said on a three-day visit to South Sudan that he feared the situation in the world's newest country - where renewed fighting in July killed more than 300 people - could worsen.South Sudan was founded with optimistic celebrations in the capital on July 9, 2011, after it gained independence from Sudan in a referendum that passed with nearly 100% of the vote.The country descended into conflict in December 2013 after President Salva Kiir accused First Vice President Riek Machar of plotting a coup.Civil war broke out when soldiers from Kiir's Dinka ethnic group disarmed and targeted troops of Machar's Nuer ethnic group. Machar and commanders loyal to him fled to the countryside, and tens of thousands of people died in the conflict that followed. Many civilians also starved.The rivals signed a peace agreement late last year, under which Machar was once again made vice president.But renewed fighting has seen Machar go into hiding, and a member of his opposition - Taban Deng Gai - take his place as First Vice President. Machar rejects the appointment, while Kiir has no objection.The latest setbacks are putting the fragile peace plan at risk.The UN says that close to five million people are hungry, and South Sudan's high inflation rate makes steep food prices unaffordable to many.Up to 60 000 people have fled to neighbouring Uganda, the UN says. About 1.6 million are internally displaced.Could get worse before it improves"The humanitarian situation here, as elsewhere in South Sudan, has the danger of getting worse before it can get better," O'Brien said at a medical centre in Aweil. "It is up to us now to partner with the people of South Sudan to have a future and to have hope."He said that the country's transport links were challenging and that "feeder roads", which are essential to infrastructure, "aren't there".Fighting between troops loyal to President Salva Kiir and those loyal to his rival, the former Vice President Riek Machar, is ongoing.Al Jazeera's Hiba Morgan, reporting from Aweil, said: "There is also evidence of armed groups [in Wau] looting villages, murdering civilians, and forcing young men and boys to join them." The hunger crisis is so acute, Morgan said, that some people had left their homes simply to find food.At the medical centre in Aweil, Regina Mayeul, the mother of three-year-old Ayak, who weighs less than half the average weight, told Al Jazeera: "Life has become hard; there is no money for me to buy things from the market except for some greens."I get that and give it to her [Ayak] but she [has] started suffering from anaemia. We had to go to the bush to find food. I just want my kids to have food and something to drink but I have no job."David Deng Deng, head of the city's health ministry, said: "Our threshold is supposed to be less than 50% or 50%, but now it's double. It's almost a 100%. This is an indication of the worsening conditions especially on malnutrition among children."