The Caretaker Governor of Western Equatoria, Patrick Rafael Zamoi, has called for calm in the state capital Yambio.
Officials say there has been exchange of gunfire between SPLA soldiers and an armed group in the town since last night.
Mr Zamoi says members of the armed vigilante group, locally known as the arrow boys, attacked a base last evening to try to free some of their leaders who are under police custody.
“I call upon all the stakeholders, relatives, parents, friends, church leaders, and community members to continue to engage these boys in pursuit of dialogue,” the governor said. “We need peace in this state.”
The attack comes less than a month after the SPLA signed an agreement with an armed group in the state to cease hostilities.
It is also less than a week after the governor declared an order barring the military from entering markets and residential areas with fire arms.