Juba - South Sudan released seven rebel detainees on Thursday but vowed to put on trial key leaders accused of launching weeks of fighting, a move likely to threaten a fragile ceasefire.
Both sides implemented the ceasefire last Friday, but combat has only eased, not ended, with reports of continuing clashes and a worsening humanitarian crisis that has left thousands dead and forced almost 800 000 to flee their homes.
Four leaders remain in custody in South Sudan, facing trial for attempting to topple President Salva Kiir after fighting broke out in the capital Juba on 15 December.
Kiir accused his sacked deputy Riek Machar and other former officials of fomenting a coup against his government.
Eleven ex-officials were arrested, while Machar - who denied any coup plot - fled.
Fighting quickly spread across the country. Aid groups say up to 10 000 people have been killed in the conflict, although many fear more may have died.
United Nations aid chief Valerie Amos wrapped up a three-day visit on Wednesday to the war-torn country, where she saw the results of over six weeks of bloodshed, with horrific atrocities reported to have been committed by both sides.
"The future of South Sudan rests on all the people being able to work together," she said, after a tour in which she saw food stores looted of tonnes of food aid, in devastated towns where workers were still burying those recently killed in the fighting.