JUBA – South Sudan has appointed its first ambassador to the United Nations, bolstering a small and inexperienced diplomatic corps which has been struggling to make the new nation’s case in disputes with Sudan over oil and the shared border.South Sudan seceded from its northern neighbour in July last year under a 2005 peace deal, and has been trying to build up state institutions after decades of devastating civil war.Juba had only managed to set up about half of the 22 embassies it set as its initial goal, the foreign minister told Reuters in June.Francis Deng, a respected scholar and former special adviser to the U.N. Secretary General on the prevention of genocide, has been appointed South Sudan’s permanent representative to the United Nations.Deng told Reuters he would work to improve the South’s "waning” image abroad, but that it would not be easy.Having a UN ambassador could help South Sudan gain other nations’ support in its disagreements with Sudan. The two countries have yet to work out a list of issues related to partition, and the disputes have at times turned violent.