South Sudan rebel chief misses deadline to return

South Sudan's rebel chief Riek Machar missed an international deadline to return to Juba on Saturday to become vice-president under a peace deal hoped to end war, claiming the government denied permission.

Machar, who appeared at an airport in Ethiopia ready to return home to the capital, said the government in Juba failed to grant him clearance to fly despite monitors completing the required weapons verification.

"I'm very disappointed," said Machar, wearing an open-necked orange shirt instead of military uniform, adding he hoped to fly on Monday.

South Sudan rebel leader Riek Machar ©Ashraf Shazly (AFP/File)

"We didn't get permission to land in Juba, not today and not tomorrow," he told reporters in the airport in the Ethiopian town of Gambella, close to the border with South Sudan. "The government is stalling."

- Uncertain welcome -

UN chief Ban Ki-moon has urged Machar to return to Juba "without delay", while the US, Britain and Norway -- key international backers of peace efforts -- demanded he return by Saturday.

South Sudan's civil war began in December 2013 when Kiir accused Machar of plotting a coup. The conflict has reignited ethnic divisions and been characterised by gross human rights violations.

It has included the abduction and rape of thousands of women and girls, massacres of civilians, recruitment of child soldiers, murder, mutilation and even cannibalism.

Machar, who fled for his life from Juba as war erupted with massacres carried out in the capital, said he was unsure of what welcome he faced.

"I don't know," he said.

He said he was returning to his base at Pagak across the border in South Sudan, but would return to the airport on Monday hoping to fly.

Machar was due to return to Juba on April 18 to forge a unity government with his arch-rival President Salva Kiir.

- 'Risk of further conflict' -

His failure to arrive has thrown an August 2015 peace agreement into jeopardy, with US, Britain and Norway warning in a statement late Friday of the risk of "further conflict and suffering."

International monitors completed verification of the number of weapons carried by the rebels accompanying him, diplomats said Saturday.

There was no immediate response from the government, who previously said they would clear Machar's plane to fly once the weapons-checking was completed.

Minister of Information Michael Makuei has previously said he expected Machar to arrive on Monday.

There was growing frustration among the rebel troops in Gambella, who have now been there for several days waiting to leave.

Under intense international pressure, the two sides reached agreement on Friday on the number of troops protecting Machar and the exact number of weapons they can carry.

Machar can bring with him 195 men, carrying AK-47 assault rifles as well as 20 machine guns and 20 rocket-propelled grenades.

Machar, a former rebel leader turned deputy president, started a new rebellion after being fired by Kiir in 2013, fighting his way back to office.

A 1,370-strong armed rebel force has already arrived in Juba as part of the peace deal, and government forces say they have implemented their promise to pull all but 3,420 of their troops from the city.

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

South Sudan ©AFP (AFP)

The President of South Sudan, Salva Kiir, addresses the nation from the State House in Juba in September 2015 ©Charles Atiki Lomodong (AFP/File)