Conflict erupted in South Sudan in December when President Salva Kiir accused former Vice President Riek Machar of trying to overthrow the government.
UNMISS in December said its peacekeepers conducted more than 300 patrols across the country to "collect evidence and document abuses" in Juba, the capital, and in restive Jonglei state.
The mission said in a statement Wednesday its movement in the country was now restricted, something it said was a violation of the bilateral status of forces agreement defining its mandate.
The United States helped broker the peace deal that ended Sudan's civil war in 2005, paving the way to South Sudan's independence six years later. The United Nations said, however, the situation in the country is "extremely volatile."
Fighting between warring parties in South Sudan has displaced more than 100,000 people since it began, the United Nations said.
Human Rights Watch in February said pro- and anti-government forces in South Sudan may have committed abuses that amount to war crimes.