The Sudan Tribune reported Sunday the fighting began Thursday among soldiers allied to the Sudan armed forces in Malakal and was believed to have spread to other areas outside the town by Saturday.
An unknown number were wounded, in addition to those killed, the newspaper said.
Phillip Aguer Panyang, spokesman of the southern army, told the Tribune the fighting broke out when a disagreement over military tanks escalated.
The tanks were to be transferred to northern Sudan," he said. "But, some southerners in the group wanted the tanks to remain in south."
South Sudan is expected to separate from the north following a January referendum in January in which 99 percent of southern Sudanese voted for secession.