South Sudan's best hope to end over two years of war risks collapse after rebel chief Riek Machar failed to return, peace deal monitors warned, as rebels Wednesday insisted he would still come.
"The agreement is at risk," said Festus Mogae, head of the Joint Monitoring and Evaluation Commission (JMEC), warning in a statement late Tuesday that both sides should "urgently demonstrate flexibility."
Mogae made the appeal to rivals to compromise and work together in a "spirit of reconciliation" after Machar failed to return to the capital Juba for a second day on Tuesday, prompting the UN Security Council to express "serious concern."
Machar, who fled during the massacres that erupted in December 2013 when war broke out in Juba, is set to take up the post of vice-president -- the same job he was sacked from months before conflict erupted -- and form a unity government with arch-rival President Salva Kiir.
South Sudan's information minister Michael Makuei said on Tuesday that the government had blocked Machar's flight because he wanted to bring "machine guns and laser-guided missiles" as well as additional troops in contravention of the peace agreement.
"This is a stalemate," Makuei said. "The question is, for how long shall we wait for Dr Riek Machar?"
Mogae, a former Botswanan president who heads the internationally-backed JMEC body trying to ensure the peace deal is implemented, said he hoped Machar's return "could be rescheduled within days, without further conditions."
But rebel spokesman Mabior Garang said Machar was still expected to return on Wednesday, insisting the delay was "caused by logistical and administrative issues, rather than political ones."
Tens of thousands of people have died in the fighting and more than two million have been driven from their homes.
The peace deal is already months behind schedule and has been repeatedly broken, with multiple militia forces paying little heed to paper agreements.