Clashes between rebels and south Sudanese troops in troubled Jonglei state have killed 105 people, a southern army spokesman said on Friday, a dramatic jump from an earlier death toll of 16.

"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 launched a spate of attacks on troops of the south's Sudan People's Liberation Army on Wednesday, 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 added.

The death toll from the fighting in Fangak town on Wednesday evening and Thursday morning, adds to an earlier toll of at least 16 dead from clashes 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 telephone, but speaking to the independent Sudan Radio Service on Thursday he accused the southern army of starting the attacks.

The renegade general launched his rebellion last year 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 cermony 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 percent 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 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.