Fighting has spread further along the Sudan-South Sudan border with 22 troops killed in a clash between soldiers from both countries.
The fighting on at a border river began after a Sudanese soldier shot a South Sudan soldier who was getting water from the river, said a South Sudan government spokesman.
That sparked a battle that killed seven South Sudan soldiers and 15 Sudan soldiers, he said. The fighting took place near the town of Meiram, along the border with Sudan's South Kordofan state and South Sudan's Northern Bahr el Ghazal state.
The clash could be a worrying sign that border violence is spreading to new regions, although the spokesman labelled the incident a "misunderstanding" and said he did not think violence would continue there.
The river battle comes amid wider violence along the shared border around the oil town of Heglig, which South Sudan troops took control of last week. Sudanese aircraft have been bombing South Sudan's Unity State as a part of that fighting.
South Sudan broke away from Sudan last year after decades of civil war. But the two sides never agreed on how to share the oil wealth found in the region between the countries, and the border was never fully settled.
Fighting has intensified in the last several weeks amid fears the two sides could return to an all-out war.