Rebel forces, including the White Army, are loyal to ousted former Vice President Riek Machar. On Tuesday, rebels attacked the town of Bor, seizing control of a nearby airstrip and part of a road that leads to the capital of Juba, 120 miles away.
Bor is strategically important, in part because it is the capital of the oil rich Jonglei state. The Sudanese army had reclaimed control of Bor last week after violent clashes with rebels. 20,000 White Army members were headed to Bor over the weekend when South Sudanese officials persuaded the militia to retreat.
Despite Tuesday's planned peace talks, the rebels are demonstrating their determination to control Bor.
The violence began in mid-December when President Salva Kiir accused his fired deputy, Riek Machar, of attempting a coup. Forces loyal to the two men have engaged in violent conflict over the past two weeks, resulting in the deaths of thousands and the displacement of 180,000.