A customs officer was wounded and three freight trucks were torched when armed men attacked the town of Nimule near the border with Uganda, officials and residents said Monday.
Nimule has remained largely unaffected by fighting that erupted around South Sudan in December 2013.
Emillio Igga, chief administrator of the area that includes Nimule, blamed rebels under the command of Major General Martin Kenyi for the attack on Sunday.
Local residents said they heard several gunshots in Rock City, an eastern suburb of Nimule, in the early hours of Sunday. Those shots were followed a few minutes later by more gunfire and huge explosions that came from Nimule airstrip and part of the town center.
Residents said the shootings lasted about one-and-a-half hours and ended at 3 a.m.
A spokesman for Riek Machar's rebel group, James Gatdet Dak, confirmed that the armed opposition was involved in the clashes.
"Our forces around Nimule town at South Sudan’s border with Uganda... preempted an attack by government forces on their positions in the area," Gatdet said in a statement.
Gatdet said the rebels launched the attack to try to force the closure of "the trade route between Uganda and South Sudan at the Nimule border unless Salva Kiir’s government accepts peace and signs an agreement with the [opposition] Movement."
He said the fighting lasted three hours, ending "when our forces withdrew from the town, after destroying government’s war logistics in the area."
Nimule is the main transit point for goods that are bought and sold between South Sudan and Uganda. Customs duties and taxes paid by traders are a significant source of revenue for the government of South Sudan.
Igga said steps are being taken to step up security in Nimule and nearby villages to prevent more attacks. Residents said several military trucks arrived in Nimule on Sunday, within hours of the attack.