In an emailed statement, the UN Mission in South Sudan (UNMISS) confirmed that armed youth and defected soldiers (SPLA in Opposition) loyal to former Vice President Riek Machar attacked Nassir Town in the Upper Nile State.The attack is “the most serious resumption of hostilities” since President Salva Kiir Mayardit and Mr. Machar met on 9 May in the Ethiopian capital of Addis Ababa and recommitted to compliance with the Cessation of Hostilities Agreement they had signed earlier on 23 January, the Mission said. Mr. Ban voiced concern that the attack “undermines ongoing intense regional and international political engagement toward a resumption of political negotiations and a peaceful resolution” of the conflict, according to his spokesperson. He called on Mr. Machar to cease immediately all offensive operations on Nassir and other points, and on the Government of South Sudan to desist from launching a counter-offensive. In the statement, Mr. Ban warned the SPLM in Opposition leadership of “the consequences” should any innocent civilian or UN peacekeepers be harmed by the forces.The Mission called the timing of the attack “deplorable” given the intensive efforts underway by mediators of the Intergovernmental Authority on Development (IGAD) to convince all parties to resume negotiations in Addis Ababa.“It is also worrying that the attack was launched in total disrespect of the presence of the IGAD Cessation of Hostilities Monitoring and Verification Team who deployed in Nassir last month,” said the acting head of UNMISS, Raisedon Zenenga.In mid-December 2013, political infighting between President Salva Kiir and former Vice President Riek Machar turned into a full-fledged conflict that has since then uprooted some 1.5 million people and placed more than 7 million at risk of hunger and disease. The conflict also sent nearly 100,000 civilians fleeing to UNMISS bases around the country.