Uganda says peace talks will continue with rebels from the Lord's Resistance Army despite reports of recent attacks.
Some 1.5m people still live in camps because of the conflict
Talks are due to resume in South Sudan shortly, with the parties expected to sign a partial agreement on reconciliation and accountability.
South Sudanese officials have complained of LRA attacks killing dozens of people in recent weeks.
The attacks were a "blatant" violation of the ceasefire, said chief government negotiator, Ruhakana Rugunda.
Uganda has given LRA leader Joseph Kony, who is wanted by the International Criminal Court, until 28 February to sign a peace deal or risk returning to war.
They are then expected to tackle the difficult issues of disarmament and reintegration.
"We will embark on a crucial stage of the talks and we will announce a date for a permanent ceasefire," Mr Rugunda said.
Last week, a Sudanese deputy provincial governor told the BBC that hundreds of rebel fighters had left assembly points and were heading towards the Central African Republic.
The Ugandan government has expressed concerns that the death of senior rebel Vincent Otti would hamper peace talks.
Otti, second in command of the Lord's Resistance Army rebels, was reportedly killed by LRA commanders last year. But his death was only officially confirmed last month.
Otti was one of four other LRA commanders wanted by the International Criminal Court (ICC) for war crimes committed during their insurgency.
Mr Kony, who has also been indicted, is in hiding in the remote north-east of the Democratic Republic of Congo but the Congolese government has ordered his troops to leave their base in the Garamba National Park.
Around 20 years of fighting with the LRA has killed tens of thousands of people and uprooted some two million people. The LRA are notorious for mutilating victims and kidnapping children to be fighters, porters and sex slaves.