Pillay and Dieng will visit South Sudan "to follow up on the recent brutal attacks against civilians in Bentiu, Unity States, and in Bor, Jonglei State, as well as to follow up on the use of radio to disseminate hate speech," Xinhua quoted UN spokesperson Stephane Dujarric as saying Friday.
"The two high-level officials are expected to meet with senior officials in South Sudan and also in the region to discuss concrete ways to help stop the violence, protect civilians against further violations of human rights and humanitarian law, as well as ensure accountability for violations and crimes committed," he said.
Opposition forces in South Sudan killed "hundreds of South Sudanese and foreign civilians" after determining their ethnicity or nationality when they captured Bentiu last week, the United Nations confirmed Monday, calling for an immediate stop to the targeting of "innocent, unarmed" civilians.
Over the past two months, thousands of people are believed to have been killed by fighting that began in mid-December as a political dispute between President Salva Kiir and his former deputy president, Riek Machar.
More than 700,000 people have been forced to flee their homes since mid-December. Another 250,000 have sought refuge in Uganda, Ethiopia, Kenya and neighbouring Sudan.