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.

South Sudan's government has denied earlier reports that Uganda had deployed special forces to its capital, Juba. Uganda's military chief Gen Muhoozi Kainerugaba said the soldiers had gone to the neighbouring country to help South Sudanese President Salva Kiir "secure" the city.

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