But the south Sudanese army said on Saturday it was their forces who had been attacked in the Balballa sector of the south's Western Bahr al-Ghazal state, by men from the army of the Khartoum-based central government.
"A company of 120 SPLA soldiers was attacked on Friday night by armed men wearing uniforms of the northern army that were heavily equipped," Major General Kuol Deim Kuol of the southern former rebel SPLA said.
The Sudanese army denied it had was involved in the fighting.
"We were not involved in these clashes," Sawarmi Khaled Saad, an army spokesman, said.
"If one of the partners in the comprehensive peace agreement has such allegations to make about the other, the joint defence council should speak about it."
Sudan's oil-producing semi-autonomous south keeps a separate army under a 2005 peace deal that ended more than two decades of civil war with the north.
Southerners will vote in referendum on whether to break away from the north on January 9, 2011.
Regional tensions
Aliou said tensions remained high in the region, which is plagued by fighting between rival ethnic groups, following Friday's clashes.
"There are many members of the Rezeigat tribe who are heading to the site of the clashes in order to help out," he said.
"There are also reinforcements from the south Sudan army coming from three cities Raja, Aweil and Wau."
More than 400 people have been killed across the south in cattle raids and revenge attacks this year, according to the United Nations.
The violence came as Sudan awaits the results of presidential, parliamentary and regional elections, which the election commission has said could be announced on Monday.
"We hope to be able to announce the result of the national presidential election, or of the presidential election for south Sudan, on Monday, God willing," Al-Hadi Mohammed Ahmed, a senior official with the national election commission (NEC), said.
Omar al-Bashir, the incumbent president, is expected to win re-election easily after most opposition parties boycotted the poll, while his National Congress Party is expected to dominate the federal government.
The Sudan People's Liberation Movement is expected to maintain its hold on the south.
