South Sudan's influential Catholic Church last month warned that the deal agreed in September to quell the country's war was falling apart and all sides were gearing for fresh fighting.

"One of the first issues that they discussed was how to bolster the ongoing peace process," South Sudan's Foreign Minister Nhial Deng Nhial told journalists after Kiir met Ethiopian Prime Minister Abiy Ahmed and Eritrean President Isaias Afwerki at State House in the capital.

Among other things, the leaders discussed bringing on board groups who rejected the deal inked in Addis Ababa, Nhial said.

"The government of the republic of South Sudan has been very supportive of this," he added.

The UN has cautioned that tens of thousands face starvation as fighting continues despite the pact.

South Sudan broke away from Sudan in 2011 after a long and bloody independence struggle, but just two years later, war broke out again when Kiir accused his former deputy Riek Machar of plotting a coup.

A conflict erupted that split the country along ethnic lines. Nearly 400,000 people are estimated to have died and millions have fled their homes, many of them pushed to the brink of starvation.

Nhial said ambassador Ismail Wais of the IGAD regional trade block monitoring the peace deal signed by Kiir and Machar, will meet separately with rebel chief Thomas Cirillo and ex-army chief-turned opposition figure Paul Malong in Addis Ababa and Nairobi on March 8 and 10.

Cirillo and Malong both rejected the September deal.

Eritrea and Ethiopia, themselves still working on healing ties damaged by years of conflict over their shared border, are part of IGAD. Both have established business investments in South Sudan's hotel industry.

Ethiopia is a key contributor to a 4,000-regional armed protection force deployed to prevent further outbreak of war in South Sudan.