At the weekend, ethnic conflict broke out in Bieh State, leaving 242 people dead.
Local authorities said over 300 others were injured in what the presidential press secretary described as a revenge attack by youth from Pibor Administrative Area.
The fighting led to the displacement of Pieri residents and suspension of medical charity MSF operations there.
In a statement issued on Wednesday, UNMISS says a patrol of military and civilian peacekeepers serving with the UN mission has reached the affected communities in the area.
“The patrol heard first-hand from local community members and military commanders about the impact of the violence, including testimony from relatives of people who were killed, injured, and fled their homes,” the UN mission said.
In February, youth from greater Akobo reportedly attacked villages in Pibor, leaving over 10 people dead.
There has been a recurrence of retaliatory attacks in Jonglei in general, mostly fuelled by cattle raids and child abduction.