An African Union committee urged South Sudan Tuesday to address outstanding "challenges" ahead of its first national election due in December and provide a clear roadmap for a credible vote.

Elections in the world's youngest nation have twice been postponed, with the government yet to implement some of the preconditions set out in a 2018 peace agreement that ended a five-year civil war.

"In the interests of national elections that are free, fair and credible, we urge the Government of South Sudan to work with speed to resolve the challenges that remain," said South African President Cyril Ramaphosa, chairman of the AU committee focused on the country.

President Salva Kiir last week dissolved the transitional government in South Sudan and appointed a caretaker administration ahead of the vote scheduled for December 22.

Electoral roadmap

The committee called for a "feasible, consensual and time-bound electoral roadmap" and for all parties to comply with the 2018 peace deal and respect a ceasefire, Ramaphosa said.

Ramaphosa said Kiir's administration must also release all political prisoners to contribute "to an inclusive political environment".

The AU committee includes South Africa, Algeria, Chad, Nigeria and Rwanda.

Addressing the meeting, Djibouti President Ismail Omar Guelleh - head of the East African regional bloc IGAD - described "significantly heightened tensions and risks of renewed" conflict.

IGAD reiterates an "urgent call" for a clear roadmap for a transition to democracy and elections, he said.

"Neither South Sudan, nor the region, nor the continent, can afford another delay," he said.