The Arab Zayadiya tribe and the Berti, a non-Arab group, have been battling with heavy weapons around the Mallit area north of El Fasher, the state capital of North Darfur.
The Zayadiya said six of their men were killed and the Berti said they suffered 13 dead, with both sides yesterday claiming the other attacked first.
"The Berti attacked Zayadiya areas" mounted on Land cruisers, leaving six members of the Arab tribe dead, their chief Abdallah Jezu told AFP by phone.
Berti leader Al-Mak Ahmedaye said his people's area had come under attack first on Tuesday.
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"They burned several villages and killed 13 of our men," he told AFP by phone.
Neither said why the fighting had taken place but Darfur's tribes and ethnic groups regularly clash over land disputes and resources.
An eyewitness in the Mallit area told AFP they had seen at least 20 bodies after the clashes, although they were unsure which side they belonged to.
Both sides used heavy weapons, the witness said by telephone.
The western region has been mired in violence since 2003 when ethnic insurgents rebelled against Khartoum's Arab-dominated government, complaining of their marginalisation.
At least 300,000 people have been killed in the conflict and more than two million displaced, according to the UN, although Khartoum puts the death toll at 10,000.
President Omar al-Bashir, who is seeking reelection in presidential and legislative polls next month, is wanted by the International Criminal Court for alleged war crimes in Darfur.