Juba - South Sudan government forces said on Monday they had seized the rebel stronghold of Pagak near the Ethiopian border, after weeks of heavy fighting that forced thousands to flee the region.
Military spokesperson Dickson Gatluak said rebel forces loyal to exiled former deputy president Riek Machar withdrew from the town on Sunday "without a fight".
He said there had been clashes in the nearby town of Maiwut, and government forces pushed the rebels back towards Pagak. Later in the afternoon the rebels withdrew from the Upper Nile town which had long been the headquarters of Machar's insurgency.
"This morning at 6am our forces entered the town and as we are speaking now they are in full control of Pagak," said Gatluak.
A spokesperson for the rebel SPLA-IO forces, Brigadier General William Gatjiath, confirmed the withdrawal from the town, but said they were now in control of Maiwut and readying to take back their stronghold.
"So at the moment as we are speaking all our forces are surrounding Pagak right now," he said.
South Sudan's civil war began in December 2013 when President Salva Kiir accused his former deputy, Machar, of plotting a coup.
Independent South Sudan analyst Alan Boswell said that Pagak had been crucial to Machar's rebellion in a conflict that largely pitted his ethnic Nuer against Kiir's Dinka.
"It is a big symbolic blow to the rebel movement. Pagak has been the general headquarters since basically the beginning of the rebellion. If it wasn't for the war having spread nationally this would possibly have signalled the end of the rebellion."
Since the collapse of a peace agreement in 2015, South Sudan's war has spread across the nation, sweeping up other ethnic groups and local grievances.
Machar was forced into exile in South Africa last year but Pagak had remained a military stronghold for his loyalists.
Tens of thousands have been killed and millions forced from their homes since the conflict began. The latest UN figures say half the population -- roughly six million people - will need emergency food aid this month.