United Nations Special Advisor for the Prevention of Genocide and Special Advisor for the Prevention of Genocide, Adama Dieng (R) flanked by the U.N. High Commissioner for Human Rights Navi Pillay address a news conference at the U.N. base in Juba April 30, 2014. A personal power struggle between South Sudan's leaders is driving Africa's newest nation to "catastrophe", Pillay said on Wednesday. The visit by Pillay was prompted by a rebel attack on the South Sudanese oil hub of Bentiu this month that left hundreds dead and a revenge assault by rivals on people sheltering in a U.N. base. REUTERS/Carl Odera (SOUTH SUDAN - Tags: SOCIETY POLITICS CIVIL UNREST)