Unknown assailants have attacked a convoy of northern Sudanese soldiers and UN peacekeepers in Sudan's Abyei flashpoint region, wounding two, the United Nations said.
A convoy of northern Sudanese soldiers escorted by UN peacekeepers came under fire on their way to Goli, north of Abyei town, late on Thursday, said a spokesman for the UN Mission in Sudan (UNMIS) on Friday, adding that the attackers were unknown.
The Sudanese army said it reserved the right to respond to this "aggression", according to a brief alert carried by state news agency SUNA. It gave no more details.
The south overwhelmingly voted to declare independence from the mostly Muslim north in a referendum in January but tensions have built up in Abyei, an oil-producing border region claimed by both sides.
The peacekeepers had escorted two companies of the Sudanese army as part of an agreement between north and south to withdraw all unauthorised forces from both sides beyond a joint force, the UNMIS spokesman said.
Under earlier agreements, only special joint north-south police and army units are supposed to patrol Abyei. But both sides have built up separate troops and heavy weapons, according to satellite images and the United Nations.
Earlier this month, at least 14 people were killed in clashes between northern and southern forces in Abyei. Both sides blamed each other for starting the violence.
Last month, Sudan's president Omar Hassan al-Bashir said he would not recognise south Sudan as an independent state unless it gave up a claim on Abyei, made in the south's draft constitution.
Sudan's north and south have fought for all but a few years since 1955 over oil, ethnicity, religion and ideology. The conflict, which ended with a 2005 peace deal, killed an estimated 2 million people and destabilised much of east Africa.
Abyei residents were also supposed to have a referendum in January over whether to join the north or south. But disputes over who could vote derailed that ballot and talks over the status of the region have stalled.