The second round of peace talks on South Sudan, scheduled to start later Monday, has been postponed, officials said.
"The talks are not resuming today," South Sudan government spokesman Michael Makuei told AFP. A government official from host country Ethiopia confirmed the postponement.
The two sides has previously agreed to meet again Monday for a second phase of negotiations on a political agreement designed to address the root causes of the unrest.
Seven South Sudanese political figures, who were among 11 arrested in Juba when the fighting broke out in mid-December and who were freed at the end of January, were due to take part in the talks, IGAD said.
The other four who were arrested -- presented as Machar sympathisers -- are still detained in Juba. The government side wants to try them, along with two other political figures -- including Machar himself -- who are the run.
The detainees had been a major obstacle to progress in the first round, and the fate of the four is set to come up again in the latest talks.
"We are still requesting, or demanding, the release of the remaining detainees," rebel spokesman Yohanis Musa Pouk told AFP.
He said the rebels would also demand that someone other than Kiir should lead the country until elections are held in 2015.
"We should have an independent person that can lead the government until we go to elections. President Kiir is not the right person at this time," he said.
But Pouk also said he was not optimistic about the success of the negotiations "because we know that our government is not serious about the talks."
The military situation in large parts of this vast country largely devoid of infrastructure remains unclear.
During the two-week break in discussions IGAD said its mediators briefed the heads of state of member countries and sought their advice.
The first IGAD monitors, tasked with checking that the ceasefire is indeed implemented, were also deployed. The ceasefire, however, has already been broken several times.
The conflict, which started in the capital Juba and which spread rapidly to different parts of the country, has left thousands dead since mid-December and has caused close to 900,000 others to flee their homes.
The conflict has also had a tribal dimension, with the two largest ethnic communities, the Dinka, to which Kiir belongs, and Machar's group the Nuer, both carrying out ethnic massacres.
Analysts warned against over-optimism on the talks.
"The negotiations are a stopgap measure at best: the institutional deficiences that have brought about the violence remain," wrote Peter Biar Ajak, director of the Center for Strategic Analysis and Research in Juba.
"For its (own) sake and the sake of this young country, the political leadership of South Sudan must complete the task it aborted of building basic institutions of governance," Ajak said in an op-ed in the International New York Times last week.