The UN’s refugee agency (UNHCR) says that 100,000 people are “trapped” in the South Sudanese town of Yei, 150km (93 miles) south-west of the capital, Juba.
The AFP news agency reports that UNHCR spokesman William Spindler told journalists that “government forces are surrounding the town and they are restricting access into the town and also preventing people from leaving”.
He speculated that they are being accused of siding with opposition forces.
In a statement, the UNHCR says it “is increasingly concerned for the safety and well-being” of those people in Yei.
It adds that in recent months, the town’s residents have been joined by tens of thousands of others who have fled fighting in the region.
A civil war broke out in South Sudan in December 2013, but Yei remained relatively unaffected, the UNHCR says.
A peace deal led to the formation of a unity government earlier this year.
But Yei was caught up in the fighting after South Sudan was plunged into a renewed bout of instability in July. This followed fighting between forces loyal to President Salva Kiir and those loyal to then-Vice-President Riek Machar.
