JUBA — South Sudan's rebel chief Riek Machar has agreed to attend direct talks with President Salva Kiir to end a four-month long civil war, UN Secretary-General Ban Ki-moon has said.Ban, who landed in war-torn South Sudan on Tuesday, told reporters that Machar promised he "will be present" at talks in the Ethiopian capital.Both sides in the conflict have been accused of widespread ethnic massacres, rape and the recruitment of thousands of child soldiers.