At least eight people were killed in an attack by an armed group in the disputed Abyei region on the border between Sudan and South Sudan, according to the UN peacekeeping force in the region.
In a statement on Monday, the UN Interim Security Force for Abyei (UNISFA) said its forces could not arrest the attackers.
"UNISFA calls for restraint and calm among communities in the Abyei area following the violent incident," it said.
"UNISFA troops have conducted search operations, as well as an investigation of the incident, but the perpetrators have proved elusive so far," it added.
There was no claim of responsibility for the attack.
South Sudan seceded from Sudan in an acrimonious split following a 2011 referendum.
The two nations have disputes over several issues including the status of disputed oil-rich Abyei area and South Sudan's alleged support to Sudanese rebels.
