Uganda has deployed special forces in South Sudan's capital Juba to "secure it", Uganda's military chief said on Tuesday, as tensions between South Sudan's president and first vice president stoke fears of a return to civil war.

Tension mounts in South Sudan as power deal between President Salva Kiir and Vice President Riek Machar unravels.

Uganda has deployed an unknown number of troops to South Sudan in a bid to protect the fragile government of President Salva Kiir as a tense rivalry with his deputy threatens a return to civil war in the east African nation.