Twelve civilians have been killed by members of a militia in the oil-rich Abyei region, the authorities in South Sudan are reporting.
In an official statement, South Sudan accused neighbouring Sudan of assisting the Misseriya militia in the attack early on Sunday.
The Sudanese government has not commented.
The Abyei region has long been claimed by both countries and has seen frequent clashes between people from the Dinka ethnic group and the Arab Misseriya militia.
Since 2011 a UN peacekeeping force has been based there.
The UN recently said relations between the two communities were tense and described the area as both volatile and unpredictable.