South Sudanese authorities imposed a curfew across the whole northwestern state of Wau on Tuesday, the deputy governor said, a day after at least 16 civilians died in clashes in its main town.
Residents said ethnic militias aligned to the government in the country's civil war searched house to house for members of other groups in Wau town on Monday.
The army said the violence erupted after a mutiny among soldiers guarding Wau's prison, and it was waiting for more information on what happened.
"The curfew will be there until the situation stabilises," deputy governor Charles Anthony told Reuters by phone, without saying how it would be imposed across the vast, remote territory.
The United Nations said thousands of residents, mostly women and children, took shelter in a civilian encampment protected by its peacekeepers, and another run by the Catholic church.
Anthony said the situation had now been brought under control, allowing locals to start returning to their homes, though one local social activist said people were still moving to the protected areas.
South Sudan descended into civil war in 2013 after President Salva Kiir, a Dinka, fired his deputy, Riek Machar, a Nuer. Fighting since then has often split the oil-producing country along ethnic lines and created a patchwork of armed factions.
The country is awash with weapons after decades of conflict with neighbouring Sudan and local feuds over land.