The UN is investigating clashes that have broken out in Sudan’s oil-producing state of South Kordofan.
The volatile region is on the northern side of the border with South Sudan but is home to many who fought for the south in Sudan’s long civil war.
Tensions have been rising ahead of South Sudan’s formal independence from the north in July.
Flashpoint issues include the exact position of the common border and the fate of the disputed Abyei region.
UN officials in Sudan said gunmen looted weapons from a police station in Kadugli, South Kordofan’s capital. Hours later there was a gunfight in a village about 48km (30 miles) from Kadugli.
It was not clear if the two events were connected.
South Kordofan is controlled by the north but is home to many southern-allied soldiers. The state was on the front lines during Sudan’s protracted civil war.
The governing party in South Sudan, the Sudan People’s Liberation Movement (SPLM), blamed northern military forces for the clashes.
They said the fighting involved northern soldiers rebelling against orders to disarm the southern-allied soldiers.
Analysts say the Khartoum government in northern Sudan is trying to assert its authority over the border regions ahead of South Sudan’s formal declaration of independence, scheduled for July.
A January referendum on its independence was the result of the 2005 peace deal that ended the civil war.
On 21 May, northern troops and militias entered the disputed border region of Abyei. Tens of thousands of people have fled as homes have been looted and burned.
Khartoum has ignored a call from the UN Security Council to withdraw its troops from Abyei.