AFP, Juba :Top UN aid chiefs have begged donors to increase efforts to stave off looming famine in South Sudan, where a third of the population are in crisis after months of war.Nearly a million children aged under five face acute malnutrition, the World Food Programme (WFP) and UN children’s agency UNICEF said in a joint statement released late Friday, after their top directors visited the impoverished nation.”They fear the world is allowing a repeat of what occurred in Somalia and the Horn of Africa just three years ago; when early warnings of extreme hunger and escalating malnutrition went largely unheeded until official famine levels were announced,” the statement read. Without swift action, 50,000 children could die from malnutrition this year, they added.”The world should not wait for a famine to be announced while children here are dying each and every day,” top UNICEF director Anthony Lake said.The UN Security Council said Friday the food crisis is now the worst in the world, as it called on countries who had pledged 618 million dollars in aid to make good on their promises.