South Sudan's rebel leader Riek Machar was vice-president from 2005 until he was sacked in 2013
Juba (AFP) - South Sudan rebel chief Riek Machar will miss an international deadline on Saturday to return to the capital to take up the post of vice president, the government said, with his arrival now expected next week.
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.
Machar was due to return to the capital Juba on April 18 to take up the post of first vice president alongside his arch-rival President Salva Kiir.
His failure to arrive has thrown an August 2015 peace agreement to end over two years of intense civil war into jeopardy.
But Minister of Information Michael Makuei said the government would only clear Machar's plane to arrive from Ethiopia after international monitors have verified the number of weapons carried by the rebels accompanying him.
"There is no coming today," Makuei said.
The rebels, who were at Ethiopia's Gambella airport, said they were ready to fly but needed permission to do so.
An AFP reporter at the airport said there was growing frustration among the rebel troops, who have now been there for several days, waiting to leave.
- 'Risk of further conflict' -
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.
Rebel spokesman James Gadet said the weapons had already been checked by Ethiopian officials, and could also be verified upon their arrival in Juba.
"The forces are ready," Gadet said, adding they were asking the government "to drop the issue" of independent weapons verification in Ethiopia to speed up the process.
"If they resolve the issue of the verification and they give the landing permission of the plane then they can go," he said.
The US, Britain and Norway had on Friday appealed for Machar to return.
"Machar's failure to go to Juba, despite efforts from the international community to support his return, places the people of South Sudan at risk of further conflict and suffering," the trio said in a statement.
"We will pursue appropriate measures against anyone who further frustrates implementation of the peace agreement."
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, 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.