Some rebels are taking part in peace talks, but the SLA is not
Sudanese soldiers have been fighting with rebels in the Darfur region in recent days, the army has confirmed.
The clashes, in Korma in northern Darfur, were the first major battles since a UN commander said last month that the region was no longer at war.
The joint African Union-United Nations force Unamid is investigating.
Sudanese officials say 10,000 people have died since the conflict broke out in 2003. The UN says 300,000 have died and 2.7 million have been displaced.
From 2003 to 2005, when the conflict was at its height, aid agencies labelled the situation in Darfur as the world's worst humanitarian crisis.
A faction of the main rebel group, the Sudan Liberation Army (SLA), said the latest clashes broke out on Thursday and continued into Friday.
The group said 20 civilians were killed during the fighting.
In a statement, the Sudanese military confirmed the clashes but said nothing about casualties.
The statement said only that government forces had "purged the areas of the remnants" of the SLA.
None of the claims have yet been independently verified.
Unamid said it was planning to send an investigation team to the area.
"We are waiting to sent an urgent mission there to verify and assess the security and humanitarian situation," said spokesman Nourredine Mezni.
The clashes are the first of any note since Unamid's outgoing military commander Gen Martin Agwai said the war in Darfur was effectively over.
The Nigerian officer characterised the violence in Sudan's Western province as closer to criminality than an outright war.
Next month peace talks on Darfur will continue in the Qatari capital Doha.
But the BBC's James Copnall in Sudan says Abdel Wahid Mohamed el-Nur, leader of the SLA faction involved in the recent clashes, has made it clear he is very unlikely to attend.
On Sunday President Omar al-Bashir appealed to all the armed movements in Darfur to join the talks.
He called on "the remaining sons of Darfur who took up arms against the government" to stop fighting and join the peace process.
The war broke out in the arid and impoverished region early in 2003 when rebel groups attacked government targets, accusing Khartoum of oppressing black Africans in favour of Arabs.
Pro-government militiamen hit back with brutal force, which the US and some rights groups have labelled genocide.
Khartoum denies supporting the militias, but the international court in The Hague issued an arrest warrant earlier this year for Mr Bashir, accusing him of war crimes.