Khartoum: 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.

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.