The Sudanese army says it has battled rebels aligned with newly independent South Sudan in a key border state.
The clashes broke out late Thursday in the town of al-Damazin in Blue Nile state, and each side has accused the other of instigating the violence.
The Sudanese government said Friday it pushed back forces traditionally seen as loyal to South Sudan's dominant Sudan People's Liberation Movement (SPLM ).
The SPLM's northern branch claimed the Sudanese army attacked positions held its forces.
The latest unrest has raised concerns that fighting between the two sides is spreading from Sudan's Southern Kordofan state, which is also located along the border.
Clashes have escalated in some border regions since South Sudan declared independence from the north in July.
Blue Nile and Southern Kordofan states are in Sudan, but many who supported the south during a 21-year civil war still live there.
Sudanese President Omar al-Bashir called for a truce in Southern Kordofan state in late August, after the United Nations said it had reports indicating that Sudanese forces were committing human rights abuses against southern supporters.
Click the link below to hear a report about the conflict in Blue Nile state by VOA's Khartoum reporter, Alsanosi Ahmed.