With ethnic-based killing spreading throughout the country, South Sudan is in danger of exchanging its current distinction as the world’s newest nation for a distinction far less welcome: home to the world’s newest civil war.

An expanded United Nations peacekeeping contingent has been charged with keeping apart the armed forces of two rival ethnic groups, the Dinka and the Nuer. But it can’t do that in the absence of an agreement by their leaders to stand down. It is thus essential that President Salva Kiir, a Dinka, and former Vice President Riek Machar, a Nuer, meet and negotiate a truce.

There is a practical obstacle to this plan, aside from the mutual distrust between the men and their tribes: Machar has insisted he be represented in talks by a third political figure. That plan, in turn, is hampered by another inconvenient fact: This man, along with 10 others, is in jail -- accused of plotting to overthrow the president.

If Machar, whose whereabouts are unknown, were accessible, South Sudan’s well-wishers could pressure him to drop this demand. In the meantime, Kiir has refused to free the political leaders arrested in the putative coup attempt.

U.S. Special Envoy to South Sudan Donald Booth and other interlocutors should lean on Kiir to reconsider. The president has produced no evidence that this month’s clashes between members of the presidential guard were part of a coup attempt, although afterward Machar publicly called on the army and the ruling party to end Kiir’s rule. Instead, the fighting among the guards has been traced to an order -- of unknown provenance -- that Dinka members disarm their Nuer counterparts. Which may well be proof of the mutual suspicion and ill will between South Sudan’s two largest tribes, but it does not seem like a precursor to a Nuer overthrow of a Dinka president.

So what to do? Kiir has already agreed to meet Machar, who is accused of leading the coup plot. Given that stance, it’s hard to see what the president stands to lose by releasing the 11 prisoners. If they have committed offenses, there will be time later for that accounting. Meanwhile, by making this concession, Kiir would put the onus on Machar to follow suit and gain the goodwill of the diplomatic community, if not his own people.

Machar, who once harbored ambitions to replace Kiir, almost surely has sabotaged his political career by pushing for the president’s unlawful removal. The best future for him now is to be the Nuer leader who led South Sudan away from the precipice of civil war. It’s up to Kiir to be clever enough to take that walk with him.

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