Twenty Sudanese soldiers and 43 Darfur rebels were killed in fierce clashes over a Sudanese army base close to the Chadian border, the country's army said on Monday.
Darfur's rebel Justice and Equality Movement (JEM) said it attacked the army base in the settlement of Umm Baru, in north Darfur on Sunday, the second military camp it has raided in just over a week.
The region's joint UN/African Union UNAMID peacekeeping force originally said the rebel attackers had overrun the army base.
But UNAMID Information Director Kemal Saiki said on Monday the reports from peacekeepers also based in the settlement had been confused.
"They did make a push for it, but they did not overrun the post. Put it down to the fog of war," Saiki said.
UNAMID later released a statement condemning the violence, adding 350 civilians and 100 government soldiers took refuge close to its own base in Umm Baru during the clashes.
"Urgent humanitarian aid, particularly food, water, medical supplies and tents, is needed to help civilians displaced by the fighting," the statement added.
UN Secretary General Ban Ki-moon said he was gravely concerned by the fighting and urged both sides to seek a negotiated settlement.
"Noting that this clash was reportedly initiated by the JEM, the Secretary-General condemns such military action, which puts civilian lives directly at risk and which seriously undermines efforts to achieve a peaceful end to the conflict in Darfur," a UN statement said.
Sudan's army spokesman Brigadier Uthman al-Agbash told state media that government soldiers had routed the rebel forces and 43 JEM fighters had been killed and 54 injured. He told the Sudanese Media Centre 20 of his soldiers had also been killed and 31 injured.
"The remnants of JEM's armed forces have fled to the Sudan-Chad border," he said. Khartoum accuses its neighbour Chad of backing JEM.
JEM gave varying accounts of the fighting. Senior commander Suleiman Sandal insisted JEM was still largely in control of Umm Baru on Monday morning and had sent out units to confront an expected government counter-attack from the south and east.
JEM humanitarian chief Suleiman Jamous told Reuters the rebel forces had pulled out of the settlement after government planes started bombing the area.
"We wanted to save the people of Umm Baru from the bombing. We pulled out after we achieved what we set out to achieve, which was to attack the base and limit the soldiers' ability to harass civilians," Jamous said.
Darfur's six-year conflict flared when mostly non-Arab rebels took up arms against Sudan's government, accusing it of neglecting the development of the region.
Estimates of the resulting death toll range from 10,000 according to Khartoum, to 300,000 according to the UN's Undersecretary-General for Humanitarian Affairs John Holmes.
Tensions have been building along Sudan's remote border with Chad for weeks. The two oil producers have long accused one another of supporting each other's rebels.
JEM said it seized a Sudanese army base at Kornoi, a settlement just 50 km (30 miles) west of Umm Baru, on May 16, along a road that runs toward a crossing point into Chad.
There have been signs of JEM re-arming and re-grouping in North Darfur in recent weeks. It fought former rebels aligned with Sudan's government around Umm Baru earlier this month.