South Sudan's President Salva Kiir has dismissed his intelligence chief and two of the country's vice-presidents, replacing one of his closest allies with a senior advisor whom analysts believe Kiir may be readying to succeed him.

South Sudan has five vice-presidents as part of a 2018 peace agreement to end a civil war. The oil-rich nation became the world's newest country in 2011 after seceding from Sudan - but it was then engulfed by civil war after Kiir and his deputy Riek Machar fell out.