Peace deal monitors in South Sudan said an unexplained delay of a rebel leader's return to the capital Juba to form a unity government with his rival President Salva Kiir was endangering an agreement aimed at ending more than two years of violence.
Riek Machar was due to arrive in Juba on Monday and sworn in as first vice president under a deal signed in August. But a spokesman for his rebel group on Monday said logistical reasons had delayed his return, causing the United States and the United Nations to express concern.
Kiir's decision to sack Machar as his deputy in 2013 precipitated the crisis that erupted into conflict in December that year. Fighting often ran along ethnic lines, pitting Kiir's dominant Dinka ethnic group against Machar's Nuer.
"The agreement is at risk. Having come so close to the formation of the transitional government of national unity, all parties must ensure that the spirit of reconciliation, compromise and dialogue embodied by the agreement should be protected," Festus Mogae, chairman of the Joint Monitoring and Evaluation Commission (JMEC), said in a statement late on Tuesday.
The JMEC includes members of the South Sudanese government opposition, the African Union, United Nations, European Union, and representatives from South Africa, China and the United States.
Thousands have been killed and more than two million people in a nation of 11 million have been driven from their homes since the conflict began barely two years after South Sudan's independence.
The JMEC statement said Mogae had expressed his disappointment at Machar's failure to fly to Juba from Pagak near the border with Ethiopia despite a chartered flight being offered on April 18 and 19.
"The chairperson expressed his hope that the flight of the First Vice President-designate could be rescheduled within days, without further conditions, to ensure the timely formation of the transitional government of national unity," the statement said.
It added that JMEC was to hold a meeting on April 21 to further discuss the matter.
JMEC comprises members of South Sudan's government opposition, rights groups, the African Union, United Nations, European Union, regional grouping IGAD.
It also includes representatives from Ethiopia, Djibouti, Kenya, South Africa, China, Norway, United States and United Kingdom among others.