About one-third of the population in newly independent South Sudan faces a "gathering storm of hunger," the UN's World Food Programme warned on Thursday. The agency said it is scaling up operations to support 2.7 million people short of food and affected by conflict. "A gathering storm of hunger is approaching South Sudan," WFP's country director, Chris Nikoi, said in a statement that reported food prices have already doubled or tripled in some areas. South Sudan seceded from the north in July after decades of civil war that left the nation of largely subsistence farmers in ruins. "Crop failure following erratic rains has led to very high food prices, aggravated by conflict, market disruption from border closures and an increase in demand from returnees and displaced people," WFP said. It called "urgently" for about $92 million (71 million euros) to address hunger in the first four months of 2012. UN agencies have predicted a grain shortage of around 400,000 tonnes next year in the country which needs to produce one million tonnes of food annually. In October, Commerce Minister Garang Diing Akuong said South Sudan had never been able to feed itself. Most supplementary food had come from the north but borders had been blocked since May after Khartoum occupied the contested area of Abyei, he said. "Conflict and growing insecurity -- particularly the use of landmines -- is combining with already poor road infrastructure to hinder humanitarian access," WFP said. Rebel groups suspected of laying mines have become increasingly active in northern, oil-rich states since the start of the year, when South Sudan voted overwhelmingly for independence in a referendum. When the south seceded it took 75 percent of Sudan's oil production, but Juba and Khartoum are in dispute over how to share revenues. Southern officials accuse the Sudanese government of trying to start an "oil war" by funding rebels in Unity and Upper Nile states, charges repeatedly denied by Khartoum. Sudan claims the south is funding rebels formerly aligned to its guerrilla army in Blue Nile and South Kordofan states. Tens of thousands of refugees have streamed over the border fleeing aerial bombardment and violence, further compounding food shortages. WFP said funds must come soon so that it can move food before April, when rains render up to 60 percent of the landlocked country inaccessible.