At least 10 people were killed in clashes between Arab nomads, militia fighters and police in Sudan's flashpoint Abyei region, officials said, in the first report of significant violence since a tentative peace deal.
Both north and south Sudan claim the oil-producing area of Abyei, one of the most likely sources of potential conflict in the build-up to the secession of southern Sudan, due in July.
Fighting in Abyei -- between Misseriya nomads, linked to the north, and the south-linked Dinka Ngok people -- marred the start of voting in a referendum in January that saw the south vote for independence.
Later in the month, both sides reached a deal promising to pay blood money for earlier clashes and open up migration routes for livestock. Northern and southern leaders promised to hammer out a settlement on who owned Abyei.
Abyei's chief administrator Deng Arop Kuol, from the Dinka Ngok, told Reuters a group of Misseriya, backed by militia fighters, attacked the settlement of Todach in the early hours of Sunday morning.
Kuol said the militia were part of the Khartoum-backed Popular Defence Forces. There are senior figures in the government who are inciting people to fight ... We don't know really what they are aiming at. Do they want to disrupt the (north-south border) demarcation process, or the process of the separation of the south?
Senior Misseriya official Saddig Babo Nimr accused south Sudan's army of starting the fighting by attacking a nomadic camp north of Abyei, adding the fighting continued on Monday.
You would have to ask the SPLA (southern army) why. From my perspective, they want to evacuate the area of Arabs ... I think the Misseriya are reinforcing.
No one was immediately available to comment from the government or the northern army. Both have denied accusations of arming the Misseriya and allied militias in the past. The south's army denied any involvement.
Kuol said around seven police officers in Todach, and around three of the attackers, were killed.
He said there had been little progress in rolling out the peace deal agreed in Kadugli, the capital of the surrounding state of Southern Kordofan. Sunday's clash came days after a meeting between Dinka and Misseriya leaders over compensation and migration routes ended without agreement, he added.
Abyei was a battleground in the decades-long civil war between north and south Sudan that ended in the 2005 Comprehensive Peace Agreement -- an accord that promised the southern secession referendum.
Abyei residents were promised their own vote on whether to join the north or south. That plebiscite never took place after disagreements over who was qualified to vote and the failure to agree on the members of an organising commission.
Northern and southern leaders were due to meet in the Ethiopian town of Debre Zeit this week to try and resolve other issues, including the division of national debts, the position of their shared border and payments for transporting southern oil through the north to Port Sudan.