The Sudanese military on Saturday denied bombing civilians in an operation which rebels said left 16 villagers and five government troops dead near the South Sudanese frontier.
Four rebels were wounded and "less than three" killed in the fighting, Mubarak Abdelrahman Ahmed, of the rebel youth wing in South Kordofan state, told AFP by satellite telephone.
Oil-producing South Kordofan remained under Khartoum's administration when South Sudan became independent in July, but fighting since June has pitted Nuba rebels, once allied to rebels in the South, against the Sudanese army.
The latest action began on January 7 with aerial bombing at Angola village that left nine civilians dead and 26 wounded, followed the next day by bombing around Al-Buram that killed seven, Ahmed alleged.
The areas are about 30-40 kilometers (19-25 miles) north of the poorly-defined north-south border. Access to the region is restricted, making independent verification difficult.
Sawarmi Khaled Saad, the Sudanese army spokesman, denied any bombing occurred but said government troops had conducted a "wide operation" that expelled rebels from the area and reopened a road.
"We don't have figures for dead or wounded" on either the government or rebel sides, he said.
The rebels' Ahmed said Sudanese troops moving from the state capital Kadugli captured the former garrison of Tess last Monday "but we retook it immediately."
As the troops moved east to Al-Buram, the main battle occurred on Tuesday and Wednesday, he said.
"We destroyed one complete convoy ... five big trucks carrying ammunition and guns", while four other trucks were captured and the bodies of five government soldiers left on the ground, Ahmed said. A similar conflict is going on in nearby Blue Nile state.
The United Nations says hundreds of thousands of people have become internally displaced or otherwise severely affected because of fighting in the two states.
Refugees fleeing to Ethiopia and South Sudan are reporting food shortages and rising levels of malnutrition, with "particularly alarming" signs coming from rebel-held areas, Valerie Amos, the UN's top emergency aid official, said during a visit to Khartoum this month.
The government, citing security concerns, continues to bar UN and foreign aid workers from the warzone.
South Kordofan's governor, Ahmad Harun, is wanted by the Hague-based International Criminal Court for alleged war crimes and crimes against humanity committed in Sudan's Darfur region.
Sudan and South Sudan have accused each other of supporting rebels inside their respective borders.
South Sudan became independent last July in a referendum that followed two decades of civil war.