Heavy fighting between government and rebel forces over strategic oil fields in one of South Sudan's northern provinces has prompted yet another rebuke from the UN Secretary General. The strongly worded statement was issued after four internally displaced persons were killed when two mortar bombs exploded inside a UN compound in Melut in Upper Nile State. Fighting has intensified in the last ten days between the SPLA in Government under President Salva Kirr and rebel troops loyal to sacked Vice President Riek Machar in both Upper Nile and Unity States as the opposing groups renew their fight for territorial dominance. Sherwin Bryce-Pease reports.