JUBA – Almost half the population of south Sudan is facing food shortages because of conflict and drought, a fourfold rise in the numbers needing aid since last year, officials said on Ruesday. "Internal conflict and incursions from the (Ugandan rebel) Lord's Resistance Army (LRA) together with drought have made almost half the population of the south short of food," southern Sudan Agriculture and Forestry Minister Samson Kwaje said in a statement. A total of 4.3 million need food aid in the oil-producing south, up from around 1 million last year, the UN said. A surge in tribal fighting has killed more than 2,500 people since the beginning of 2009, aid groups said, and seasonal rains were weak across much of the underdeveloped region. A census released last year showed a total Sudanese population of 39.15 million, with 30.89 million living in the mainly Muslim north and 8.26 million in the south. The south contests the census saying it undercounts southerners. The UN's World Food Programme (WFP) said violence had forced 350,000 to flee their homes in 2009, leaving them dependent on food aid. Last year's poor seasonal rains also destroyed harvests, and the area was bracing for this year's rains, which could disrupt transport, it added. "This spike in the number of hungry people in southern Sudan comes just ahead of the rainy season when roads become blocked and communities are cut off from food assistance," Leo van der Velden, coordinator for the UN's World Food Programme (WFP) in the south, said in a statement. Meanwhile, US President Barack Obama warned on Tuesday the United States would increase pressure on Sudan's government if it did not respond to a US engagement push aimed at securing a peace deal in Darfur. Obama, in a question and answer session broadcast on YouTube and the White House website, said he hoped the Khartoum government would accept efforts to broker a deal with rebels to end the human tragedy in the region. "We continue to put pressure on the Sudanese government," Obama said. "If they are not cooperative in these efforts, then it is going to be appropriate for us to conclude that engagement doesn't work and we are going to have to apply additional pressure on Sudan in order to achieve our objectives."