Southern Sudanese troops said militias supported by northern Sudanese soldiers mounted a new attack on them today, threatening a fragile peace deal.
It was the latest strain to the rocky 2005 peace agreement that ended a north-south civil war, Africa's longest, which killed 2 million people.
"They attacked our people again at 9:30am in the morning, but they have been repulsed," said James Hoth, a major-general in the former rebel southern Sudan People's Liberation Army (SPLA).
Both sides accuse the other of breaking the peace pact, which enshrines democratic transformation, power and wealth sharing and a southern vote on independence by 2011.
Southern Sudan's Presidential Affairs Minister Luka Biong said the attack close to the oil-rich north-south border was launched by tribal groups, supported by disaffected Sudan Armed Forces (SAF) soldiers and other militias who wanted a return to conflict in the region.
"This is a group of the Popular Defence Force (militia) and SAF forces," Mr Biong said. "It will affect the peace."
He said the SAF soldiers had encouraged members of the nomadic Misseriya tribe to launch the assault. The reports on Friday came after dozens were killed in two similar attacks on southern positions in the last week of December.
No one was immediately available for comment from Sudan's armed forces. But the army has repeatedly denied involvement in the skirmishes. Misseriya leaders have previously accused the SPLA of starting the clashes.
Northern militias, including the Popular Defence Forces, were mobilised by Khartoum in the south to back its war efforts.
The peace agreement has largely held but both sides have been caught up in protracted political wrangling, each accusing the other of breaching key parts of the peace deal.
One major complaint has been northern troops' failure to quit the south by a July 9th deadline. Southern officials accuse northern forces of remaining in southern oil areas to retain control of Sudan's main export.
Crisis talks first set a new withdrawal date for December 15th and then moved the deadline to the end of 2007. SPLA officials said the withdrawal deadline had been moved again to Jan. 9.
Mr Biong said he did not have details of the numbers of casualties in Friday's attack, which he said took place in open ground close to the north-south border south of the River Kiir.
He said the governors of the neighbouring states of South Kordofan and the south's Northern Bahr el Ghazal met on Thursday to try and find a way to end the clashes.
"But they have not been able to stop these people," he said. "They are well armed."