Tribes in Darfur claim that 55 of their tribesmen have been killed as a result of an attack by southern Sudanese, the BBC reported.
The killings are making matters more tense in the northern boarders, officials told the New York Times.
"I can't tell you who attacked who first," Muhammad Eissa Aliu, a leader of the Arab Rizeigat tribe in South Darfur, said. "It happened on Friday and those killed from the Rizeigat were 58, and 85 injured."
Aliu told the Times that his tribe fought with the south's Sudan People's Liberation Army.
Southern Sudan accused the northern government of the assault Sunday. The BBC claims it is the worst violence reported since Sudan's poll on 11-15 April.
Clashing are frequent enough over grazing rights and water points, a BBC correspondent said.
Other than the dead, at least 85 tribesmen were wounded, Aliou told the BBC.