At least 200 South Sudanese refugees were reported to have drowned in the White Nile when their barge sank as they fled renewed fighting between rebel and government forces.
The civilians, including women and children, had crowded on to the old boat in an attempt to escape across the river as rebels attacked the town of Malakal, according to reports. "The boat was overloaded," Colonel Philip Aguer, a spokesman for the South Sudanese army, said.
Between 200 and 300 people were reported to be killed. Thousands of people have fled the fighting by crossing the river, but the journey can be very dangerous. If the death toll is confirmed, this would be the biggest loss of life among refugees since the civil war began on December 15.
The incident began when, after suffering a string of defeats, forces loyal to Riek Machar, the former vice-president, struck back by attacking Malakal on Sunday. Machar's representatives claimed at peace talks in Ethiopia that the town had fallen into their hands, but there was no independent confirmation of the claim.
As recently as Sunday, the army felt confident enough about the town's security to take a delegation of foreign visitors there. However, the United Nations and other independent sources confirmed that fighting had broken out in the city. Thousands more people were fleeing their homes as a result.
Many tried to escape from Malakal, which sits on the banks of the White Nile, by boat. Some chose not to risk a river journey but to seek safety inside a United Nations base. Toby Lanzer, the UN coordinator for humanitarian affairs, said the number of refugees inside this compound had almost doubled from 10,000 to 19,000.
If the rebels have taken Malakal, this would mark a surprise recovery from their recent setbacks. Last Friday, the government recaptured Bentiu, the capital of the oil-producing Unity State. Troops loyal to Salva Kiir, the president, are now laying siege to Bor, the capital of Jonglei state, which lies across the White Nile from the town of Minkamen.
After these problems, Machar agreed to meet international mediators, including a US envoy. This was taken to indicate possible willingness to agree an immediate ceasefire. But by the time of that meeting, Machar's followers were apparently preparing to attack Malakal. If they have seized the town, the rebels now control two of South Sudan's 10 state capitals, giving them significant bargaining power in direct peace talks.