Lam Paul Gabriel told The Associated Press that Machar is returning to take part in a nationwide peace celebration on Wednesday, leading a small delegation but not bringing his own security despite concerns for his safety.
"If this peace has to be implemented we need to trust each other," the spokesman said. Machar is returning to let everyone know he is ready for peace, he added. Under the deal signed last month, Machar will be President Salva Kiir's deputy once again. That arrangement has twice collapsed in deadly fighting, once when the civil war broke out in December 2013 and again in July 2016 when an earlier peace agreement collapsed and Machar fled into neighboring Congo.
Concerns are high that this latest fragile agreement will fall apart as well, with the United States among those openly wondering whether the two men whose rivalry has led to so much bloodshed can finally end the conflict.
South Sudan's five-year civil war has killed almost 400,000 people with violence and disease, according to a recent estimate. Millions have been displaced and parts of the country have been plunged into famine.
So far the new peace deal has been criticized for its slow implementation, with missed deadlines and continued cease-fire violations. Machar wrote to Kiir last week saying he would attend Wednesday's celebrations only if certain conditions were met, including the release of all political prisoners, the lifting of the state of emergency, free movement inside the country for all opposition groups and a guarantee for his safety.
While there has been no indication by South Sudan's government that the concerns have been met, Kiir in an interview with Kenyan's Citizen TV last week said Machar's safety would be secured by the government.
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