A month after southern Sudan voted overwhelmingly in favour of independence, more than 100 people have died in fighting.
There has been a series of clashes between the army and rebels. Some 39 of those killed were reported to be civilians.
The latest occurred on Wednesday afternoon and continued on Thursday in Jonglei, the south's most populous state.
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.