New York - Secretary-General Ban Ki-moon says the hopes for South Sudan when it became independent four years ago have turned to despair.
Ban says that's because the world's newest nation has become engulfed in conflict with "unconscionable levels of violence and unspeakable sexual abuse".
In a statement on Wednesday on the eve of the independence anniversary, the UN chief urged President Salva Kiir and former vice president Riek Machar "to prove their leadership" by finding a political solution and immediately concluding a peace agreement.
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He also said the international community must take decisive steps to help end the fighting.
Fighting broke out in South Sudan in December 2014 after Kiir accused Machar of trying to oust him. That sparked months of ethnic attacks, and the violence has continued despite several cease-fires.