The South Sudanese army shot and killed 10 protesters in Wau, over the weekend.
The demonstrators were angered over the move of the local council's headquarters from Wau, the capital of Western Bahr el Ghazal state, to Bagare, a smaller settlement nearby, BBC News reported.
The forces were reportedly called in to dismantle road blocks set up by the civilian protesters, Reuters reported.
Troops first opened fire on the demonstration Saturday night, killing four. They killed another six people at a second demonstration on Sunday.
The army's decision to shoot at protesters "demonstrated excessive use of force," said UN peacekeeping mission spokesman Liam McDowall, according to Agence France Presse.
UN peacekeepers had reportedly been working with both demonstrators and the army to try and establish calm, AFP reported.
"A number of protestors fled to the cathedral where they took sanctuary," McDowall said.
The South Sudanese Army, made up largely of former guerrilla fighters and militiamen, is often accused of committing human rights abuses, Reuters reported.
"We are investigating the allegations of armed elements inside the demonstrations, as well as allegations of the disproportionate use of force by the army against civilians," Kella Kueth, an army spokesman, told AFP.
More from GlobalPost: UN human rights worker expelled in South Sudan