Attacks by a renegade militia in south Sudan's Jonglei oil state killed at least 211 people, a minister for the region has said, doubling earlier estimates of the death count.
The violence has reignited concerns for the security of the underdeveloped region where voters last month overwhelmingly voted for independence from the north in a referendum.
South Sudan's army said forces loyal to George Athor, a former army officer who launched a revolt after losing in last year's elections, carried out attacks in Jonglei last week.
French oil group Total leads a consortium controlling a largely unexplored oil concession in Jonglei.
Army and government officials yesterday said the scale of the carnage emerged after searches found the bodies of civilians, including women and children, in remote areas.
Pagan Amum, secretary general of the south's dominant Sudan People's Liberation Movement (SPLM), repeated accusations that Khartoum was trying to destabilise the south by arming militias, but he stopped short of directly implicating northern government figures.
"It was a massacre of our people and it is really very painful," he said. "We are a society that is traumatised … Guns are in a lot of hands.
"Today armed groups are being financed, being armed, being sent into southern Sudan from the north.
"You know that George Athor who just caused the massacre in Fangak, his guns are coming from Khartoum."
But Rabie Abdelati, a senior member of the north's dominant National Congress Party (NCP), denied the accusation.
"Athor's is a southern group and there is no connection between the NCP and Athor," he said.
Southern government minister James Kok, who had just returned from Jonglei, said 211 people died in the fighting or later in hospital and at least 109 were wounded. His figures did not include casualties among the militias.
The dead included people who had just returned to the south to take part in the referendum, said southern army spokesman Philip Aguer.
"Some were trying to flee the fighting and drowned in the river. Some were returnees from the north who were living under trees and were caught unawares," he said.
The referendum was promised in a 2005 peace deal that ended decades of civil war between the mostly Muslim north and the south, where most follow Christianity and traditional beliefs.
Last month's referendum was largely peaceful and the NCP, led by president Omar Hassan al-Bashir, said it accepted the result. The south is due to secede officially on 9 July.
The latest killings underline the deep ethnic and political divides that remain in the south.Death counts topping 100 were reported in a spate of clashes between tribal groups and militias in 2009 and early 2010.
George Athor was a senior member of the then rebel southern army during the civil war. He stood for the governorship of Jonglei as an independent in last year's general elections and took to the bush after losing, accusing the SPLM of fraud.
Two million people were killed and four million fled during the civil war fought over ideology, oil, ethnicity and religion.
The fighting also set tribe against tribe in the south, with the north backing militias from rival ethnic groups.