A spate of attacks by rebels against the South Sudanese Army in the region's troubled Jonglei state killed 105 people, 39 of them civilians, an army spokesman said on Friday, leaving a hard-won truce in tatters.
"On the side of the military that includes the SPLA, the police and the prison services, 20 were killed in Fangak town, while 30 of Athor's men were killed," Philip Aguer told AFP.
He was referring to renegade southern general George Athor whose supporters attacked troops of the South's Sudan People's Liberation Army on Wednesday evening shattering a "permanent ceasefire" they signed just last month.
"Sadly, there were 39 civilians killed, including women and children, and 65 others wounded," as well as 30 wounded SPLA troops, Aguer said, adding that the fighting had now halted.
The latest reported deaths from clashes in Fangak town on Wednesday evening and Thursday morning represent a dramatic jump from an earlier toll of 16 people killed in fighting between Southern troops and the rebels in the Door area of Fangak county.
"The number of casualties is high because the attacks were a surprise. This is something we were not expecting because we trusted the ceasefire that was signed," Aguer said.
There was no immediate response from Athor when AFP tried to contact him by phone, but speaking to the independent Sudan Radio Service on Thursday he accused the SPLA of starting the attacks.
Medics at Malakal hospital, in neighbouring Upper Nile state, said that several people wounded in the fighting had already arrived and they were expecting to receive more.
"We are preparing ourselves to be ready for any help we can give to those who may come," said Tut Gony, the hospital's medical director.
Athor launched his rebellion in 2010, after claiming he was cheated in an election for the governorship of Jonglei state, the South's most populous.
Athor's men signed the January ceasefire with the Southern Army just days before a landmark referendum on independence for the South but he himself stayed away from the signing ceremony in the regional capital Juba.
Southern officials have charged he used the ceasefire period to recruit more fighters.
The attacks come just days after the formal confirmation of the results of the January 9-15 referendum, which showed almost 99 per cent of Southerners voted to secede and split Africa's largest country in two.
Previously the Southern Army had accused Athor and his men of acting on behalf of Khartoum in a bid to destabilise the south, a charge northern officials have denied.
Analysts have said that maintaining security in the fledgling southern nation, which is due to win international recognition in July, will be a major challenge.
Clashes in oil-producing Upper Nile state earlier this month killed 54 people and wounded 85, according to United Nations estimates, when southern former militiamen inside the Northern Army rebelled against orders to surrender their heavy weapons.
On Wednesday, a gunman shot dead southern minister Jimmy Lemi Milla in his office, an attack reported to be motivated by a personal dispute.