The United Nations' top human rights official said South Sudan is "close to calamity" Wednesday, calling on leaders on both sides of a civil conflict to take responsibility for the safety of civilians.

Navi Pillay, the U.N.'s high commissioner for human rights, said that she was "appalled by [the] apparent lack of concern displayed" by rebel leader Riek Machar and and the president, Salva Kiir, concerning the risk of famine in the country.

"The prospect of widespread hunger and malnutrition being inflicted on hundreds of thousands of their people, because of their [Riek and Machar's] personal failure to resolve their differences peacefully, did not appear to concern them very much," she said.

Her comments came a day after she and Adama Dieng, the U.N. special advisor on the prevention of genocide, met Machar on Tuesday in Juba.

Pillay relayed the U.N.'s concerns to Machar following a massacre on April 15 by rebel fighters who left the town of Bentiu littered with bodies after slaughtering civilians in the town mosque, the hospital and on streets.