More than 100 people are now said to have died in fighting in south Sudan after rebels attacked the army, officials say.
Earlier reports said this week's fighting had killed 16 people.
Some 39 of those killed were civilians, a south Sudan army spokesman said.
The clashes between fighters loyal to George Athor and south Sudan's army come as the region prepare for independence from the north following last month's referendum.
Some 99% of people voted to secede from the north, according to official results announced this week.
The UN refugee agency says it expects some 800,000 people to move from north to south Sudan this year.
The UNHCR said this would put pressure on the already fragile situation in the south, which is insecure and lacks basic services.
Mr Athor took up arms last year, alleging fraud in state elections, but signed a ceasefire last month just before the historic vote.
Twenty members of Southern Sudan's security forces were killed, along with 30 rebels, taking the new death toll to 105, southern army spokesman Philip Aguer said.
During the clashes, two army trucks were blown up by land mines near the town of Fangak in Jonglei state, he said.
He said Mr Athor's men attacked on Wednesday afternoon and clashes continued on Thursday.
Jonglei is the south's most populous state.
When Mr Athor took up arms last April, the south accused him of being used by the north to stir up trouble and derail the referendum - charges denied at the time by northern officials.
He agreed to the ceasefire deal with the SPLA days before the referendum vote began - although he did not attend the signing ceremony in person.
Mr Athor has blamed the SPLA for attacking his forces, but said that he was open to new talks.
"If the other side is willing, we can continue talks but if they are not willing, then I would say this is the end of the peace agreement between us and them," he told the Reuters news agency via satellite phone on Thursday.
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. Fifty-four people were killed over the weekend in fighting in Southern Sudan's Upper Nile state.
Sudan's President Omar al-Bashir has promised to accept the outcome of the referendum.
On Wednesday, Sudan's UN ambassador hinted that the International Criminal Court arrest warrant for Mr Bashir should be withdrawn as a "reward" for him accepting the south's independence.
Mr Bashir is accused of links to war crimes in a separate conflict in the western region of Darfur.
Southern Sudan is to become the world's newest independent state on 9 July.