New York - Eleven top detainees held by South Sudan's president Salva Kiir must be involved in any negotiations following a ceasefire deal on Thursday, the UN leader Ban Ki-moon said.
Ban and the UN Security Council both welcomed the accord reached in the Ethiopian capital but said Kiir and his arch-rival Riek Machar must now quickly move to a comprehensive agreement.
Ban "underscores the necessity to continue without delay a national political dialogue to reach a comprehensive peace agreement, with the participation of all South Sudanese political and civil society representatives, including the SPLM detainees," said his spokesman Martin Nesirky.
Kiir's detention of the 11 top Sudan People's Liberation Movement officials considered close to Machar was a major sticking point in the talks to end the conflict that erupted on December 15.
Under the ceasefire, the government agreed to release the 11, but has given no timeframe for the move.
A UN Security Council statement also welcomed the accord and, amid doubts that the two sides will keep to it, stressed "the importance of assuring its sustainability."
Kiir and Machar must "build on it towards comprehensive reconciliation" and settle "the root causes of the conflict".
Political tensions between Kiir and Machar, who was dismissed as vice president in July, have been simmering for a long time.
But civilians have paid a heavy price, with aid groups estimating up to 10 000 dead since December.
The council condemned attacks on civilians and "called for accountability for those that committed such acts".
It also condemned "attacks and accusations" against the UN Mission in South Sudan.