"She will be talking on the issues of peace plus the efforts that the government is doing," Makol said Wednesday.

"We will be expecting her to talk about the humanitarian situation and the efforts that the agencies are doing in the delivery of humanitarian aid," he added.

Haley said last month she wanted to salvage a tattered 2015 peace deal that collapsed in July last year, as regional mediators launch a fresh bid to "revitalise" the agreement.

South Sudan won independence in 2011. However, war erupted in December 2013 when Kiir accused his former deputy, Riek Machar, of plotting a coup.

Initially a war pitting ethnic Dinka supporters of Kiir against Machar's Nuer people, the conflict has since metastasised to include different groups and local interests.

Last week the regional Inter-governmental Authority on Development (IGAD) said it had finished consultations with a wide range of parties and is expected to announce a new round of peace talks.

Brian Adeba of the Enough Project advocacy group that closely follows the South Sudan conflict, told AFP that the new peace push came as government was particularly "intransigent to peace".

"It believes it has won the war, it has taken a lot of territory and the opposition is not in a position to retaliate," he said.

The group has called for the US -- South Sudan's single biggest aid donor
-- to impose new sanctions targeting a wider group of individuals as "leverage" for peace.

"There has to be a price for intransigence, and the US has the under-utilised policy tools to begin to exact that price," said the founding director of the Enough Project, John Prendergast. (AFP)