South Sudan Deadline for Rebel Chief's Return

International powers gave South Sudan's rival leaders a Saturday deadline to strike a deal and ensure rebel chief Riek Machar returns to the capital, peace monitors said.

If they fail to agree, the peace deal to end over two years of intense civil war would collapse, warned Festus Mogae, head of the internationally-backed Joint Monitoring and Evaluation Commission (JMEC).

In a country awash with weapons, the deal now stands or falls on how many machine guns and rocket-propelled grenades the rebel troops protecting Machar should be allowed to bring with them.

"If we are not able to reach an agreement, then it is a total breakdown," Mogae told reporters Thursday, after no breakthrough was made in an all-day JMEC meeting in the capital Juba.

Tens of thousands have been killed and more than two million have been driven from their homes since war broke out in December 2013, a conflict characterised by extreme brutality and human rights violations.

The April 23 deadline was proposed by the non-South Sudanese members of JMEC, which include the African Union and European Union, as well as China, Britain, Norway and the United States, diplomats said.

Rebel officials said Machar would return on a one-hour flight from neighbouring Ethiopia as soon possible after a deal was agreed, and then take up the post of vice-president.

If they fail, the rivals will be reported to the UN Security Council.

His return to forge a unity government with arch-rival President Salva Kiir is seen as fundamental to ensure the repeatedly delayed and broken peace deal sticks.

But his arrival on Monday was delayed by wrangling over how many soldiers and weapons he could bring with him, with the government saying his large armed entourage would contravene the peace deal.

The international proposal -- accepted by rebels -- is that Machar's guards can bring 20 machine guns and rocket-propelled grenades, while the government says the limit should be just seven.

"If there is no agreement until that day, then I am required to report to the IGAD heads of state, to the Security Council of the African Union and to the Security Council of the United Nations," Mogae said, when asked what will happen if the April 23 deadline is missed.

Minister of Information Michael Makuei told reporters that both sides were "advised to go and sleep on this and think how best we can come out with an amicable solution."

Rebel negotiator Taban Deng Gai said they accepted the international proposal.

"Once we have this approval by the government... we shall have the first vice-president to Juba as early as possible," Gai said.

The peace deal is already months behind schedule, with multiple militia forces paying little heed to paper agreements.

A 1,370-strong armed rebel force has finished arriving in the city as part of the peace deal, while government forces say they have pulled out all but 3,420 of their troops, according to the agreement.

All other soldiers have to remain at least 25 kilometres (15 miles) outside the capital.

Earlier on Thursday, more than 100 hundred rebel supporters arrived in Juba from Ethiopia, boosting hopes for Machar's return.