The White House on Monday abruptly announced the departure of president Obamas special envoy to Sudan Princeton Lyman who held the post since March 2011. Obama hailed the work done by his special envoy particularly during the transition from a united Sudan to a partitioned one in July 2011. "For the last two years, Ambassador Princeton Lyman has served as my Special Envoy to Sudan and South Sudan, building on a long legacy of dedicated service in the United States government. Princeton has done a tremendous job in helping to realize the promise of an independent South Sudan, and working toward the international vision of Sudan and South Sudan living side by side in peace" the U.S. president said according to a statement on White House website. "I have valued his extraordinary service, which has been appreciated by the United States and the international community. The people of Sudan and South Sudan, who have suffered so much, have the opportunity to seize a brighter future because of Princetons efforts to urge both sides to put the interests of their people first. I am deeply grateful for Princetons steadfast and tireless leadership, and wish him and his family well" the press release read. No reason was given for Lymans resignation and no replacement was announced. Obama starts his second term next month amid reports of major shuffles in his cabinet. The outgoing envoy replaced Scott Gration who moved to become U.S. ambassador to Kenya until he later resigned. Lyman served as ambassador to Nigeria and South Africa and was also Assistant Secretary of State for International Organization Affairs in the 90s. During his tenure Lyman worked to mediate between Khartoum and Juba to resolve the outstanding issues especially pertaining to borders, oil, Abyei status and insurgency near South Sudan borders. The U.S. has also been pressing Juba to stop its backing of Sudan People Liberation Movement North (SPLM-N) fighting Khartoum in the border states of Blue Nile and South Kordofan. The issue is main sticking point in the stalled security agreement between north and south Sudan.