South Sudanese troops were battling rebel forces yesterday for control of the key oil town of Malakal, while government forces recaptured the key town of Bor, the army said.
"Communication is still difficult. We will find out today how the fighting ended yesterday. We still feel we're still sharing Malakal with the rebels, but by the end of the day (the army) must clear the rebels from Malakal," army spokesman Philip Aguer told AFP.
"Today the gallant SPLA forces entered Bor, they have defeated more than 15,000 forces of (rebel leader) Riek Machar and frustrated his plans to attack Juba," he added.
Bor has changed hands four times since the conflict in the world's youngest nation began five weeks ago.
Ateny Wek Ateny, spokesman for President Salva Kiir, said the troops had been "congratulated for a job well done".
He also said the Sudan People's Liberation Army would "observe international rule of law".
On the other hand, both rebels and the government claim to control Malakal, the capital of Upper Nile state and one of the main battlefields since fighting erupted last month between rival forces loyal to President Salva Kiir and his sacked deputy, Riek Machar.
The United Nations said Friday that child soldiers had joined the conflict, with atrocities including war crimes committed on both sides.
The UN says 468,000 people have fled their homes because of the fighting, which has spiralled into ethnic killings between members of Kiir's Dinka people -- the country's largest group -- and Machar's Nuer.
Up to 10,000 people are believed to have been killed so far in the conflict.