The authorities in southern Sudan say nearly 70 armed Arab nomads have been killed in clashes on the border between the north and south of the country.
There are fears the fighting could threaten Sudan's 2005 peace deal
The clashes occurred between Misseriya tribesmen and fighters from the Sudan People's Liberation Movement (SPLM).
The SPLM is a former rebel force which, under a 2005 peace deal, shares power with the National Congress Party (NCP).
But SPLM claims that the NCP is backing the Misseriya have led to fears that the peace deal could be undermined.
This is the latest in a series of clashes in the oil-rich Abyei border region, which correspondents say is a potential flashpoint for renewed conflict between the north and south.
The latest clashes took place in the state of Northern Bahr El Ghazal, west of Abyei, said the SPLM, which governs the semi-autonomous south.
It said about 69 tribesmen, and six soldiers, had been killed.
But a Misseriya leader, Hassan Mohamed Sabahi, told Reuters 37 tribesmen had died, while about 62 were wounded.
Another Misseriya chief, Babu Nemir, said the tribesmen had "attacked [an] SPLM camp on border lines and destroyed it completely", the Sudanese Media Center reported.
The Misseriya said it started the fighting in retaliation for an attack by the SPLM armed wing last week.
But an SPLM spokesman, Edward Lino, accused the NCP of using the Misseriya tribe to provoke confrontation.
He said the NCP wanted to delay the demarcation of a clear north-south border in the region, as well as to prevent a national census taking place, deemed vital for the success of the country's first democratic election in 23 years.
Tensions have worsened recently in the oil-rich area, which analysts link to the failure to demarcate a clear border.
Abyei's status was left unresolved when the Comprehensive Peace Agreement was signed and has become a thorny issue between the two parties, says the BBC's Amber Henshaw in Sudan.
She says reaching a compromise looks increasingly difficult.
Both the nomads and the SPLM caution that the situation could further deteriorate if nothing is done to address the tensions in the area.
There are fears that the fighting could threaten the 2005 peace accord, and a spokesman for the United Nations mission in Sudan said it was urging the parties to find a solution.