Philip Auger, a spokesman for the South Sudanese military, told the independent Sudan Tribune that his forces were able to repel an attack by Sudanese troops.
"What I can tell you is that two brigades of Sudan armed forces, backed with 16 tanks and accompanied by members of the mujahedin and other militias loyal to Khartoum advanced toward Unity state with the intent to capture and occupy the oil fields, but our forces repulsed them toward Heglig," he said Wednesday.
Khartoum condemned the "aggressive behavior" of South Sudan's forces and said the oil field in Heglig "is not part of South Sudan."
South Sudan gained independence in July as part of a peace agreement though matters concerning oil were sidelined in favor of autonomy. South Sudan gained control over most of the oil fields in the region though Sudan governs the export infrastructure.
The Sudan Tribune said most of the workers have been evacuated from the Heglig oil field.