Some 200 people were killed in a "massacre" in south Sudan last week, officials say.
Most of the dead were civilians, including children and others chased into a river by rebels, a minister said.
Previous estimates said that about 100 people had died when fighters loyal to rebel leader George Athor attacked.
The deaths come as the region prepares for independence from the north after last month's referendum.
Some 99% of people voted to secede from the north.
A senior official of south Sudan's ruling party accused the north of backing the rebel attacks.
The north has denied previous similar accusations.
The referendum on independence for the oil-rich south was part of a deal to end decades of north-south conflict.
The south's Humanitarian Affairs Minister James Kok, who has just returned from the area, told the AP news agency that 201 people, had been killed in what he termed a "massacre".
"They were chased into the river. I was the one who put them into a mass grave," he said.
He said nearly 160 of the dead in the two days of fighting last week were civilians, such as children, the elderly, refugees and several priests.
Another senior official said 197 people had died in the fighting in Jonglei, the south's most populous state.
Mr Athor blames the clashes on the southern army.
He took up arms last year, alleging fraud in state elections, but agreed to a ceasefire last month just before the historic referendum.
The BBC's Peter Martell in the southern capital, Juba, says the fighting is another sign of the challenges the south faces in bringing its people together and improving security.
The week-long referendum vote itself passed off peacefully, but tension remains high in parts of the oil-rich area which straddles the north and south.
Sudan's President Omar al-Bashir has promised to accept the outcome of the referendum.
Southern Sudan is to become the world's newest independent state on 9 July.