The United Nations says a bombing campaign in the Southern Kordofan border state in Sudan is causing huge suffering to civilians.
Northern forces has been fighting southern groups for more than a week. The BBC reports the clashes have escalated to include artillery and aircraft.
The bombing follows a deal for both sides to withdraw from the nearby disputed town of Abyei.
South Sudan is preparing for independence next month. It has most of the country's oil fields.
Some 140,000 people have fled the fighting.
Decades of civil war ended in 2005 with a deal, under which a referendum was held in January on secession by the south. Some 99% of voters opted for independence.