Monitors of South Sudan's troubled peace agreement say government troops burned thousands of civilians' homes last year amid the country's three-year civil war.
Friday's report levels some of the strongest allegations yet against security forces in the conflict.
The report said three villages in the southern Yei region visited by investigators had been abandoned and destroyed at the end of last year.
A visit to Yei in November led a UN special adviser to warn that South Sudan could slip into genocide.
The new report says government forces denied UN officials and investigators access to one Yei village, while government officials blamed rebels for the homes' destruction. Investigators said that this was unlikely.
Satellite data from Amnesty International shows about 2,000 structures were destroyed along a highway near Yei between late December and January.