FILE - In this Monday, April 26, 2010 file photo, then Vice President Riek Machar, left, and President of South Sudan Salva Kiir, centre, arrive for a press conference in Juba, South Sudan. Mediators say President Salva Kiir of South Sudan and rebel leader Riek Machar are expected to sign a peace agreement in Addis Ababa, Ethiopia on Monday, Aug. 17, 2015, with the U.S. urging the warring factions to reach a peace agreement by that date or face sanctions. (AP Photo/Pete Muller, File)