The latest round of peace talks between South Sudan's two rival leaders has failed to strike a deal on the vital issue of internal boundaries, mediators said on Friday.
Critics have accused President Salva Kiir of reorganising state boundaries to shore up his power and the issue has hobbled talks with rebel leader Riek Machar.
South Africa's Deputy President David Mabuza, mediating the talks in South Sudan's capital Juba, said the two men had agreed to a week-long arbitration process to help resolve the dispute.
The longtime rivals, whose fallout sparked a civil war in 2013, signed a peace agreement in 2018 but have missed two deadlines to form a power-sharing government.
They have held several rounds of discussions since November, when they were given 100 more days to form a unity government.
Mabuza said the talks had concluded without an agreement over states and boundaries.
"The number of states and their boundaries has been a sticking point between parties towards the formation of a transitional government of national unity," the South African presidency said in a statement Friday.
"Given that this matter has not been settled, the parties have agreed on a seven day period for further consultation on the proposal of arbitration as a mechanism to break the impasse."
Mabuza said mediators "are confident" Kiir and Machar would meet the new February 22 deadline to form a coalition, a key pillar of the September 2018 peace deal that largely brought a pause to years of fighting.
But Machar's SPLA-IO party said Friday it would not enter a power-sharing arrangement until the outstanding matter of states was resolved.
"We didn't agree to form the government and then discuss the number of states. What we said is that we should form the government after we solve the issues of number of states and their boundaries," Manawa Peter Gatkuoth, a spokesman for the SPLA-IO, told AFP.
When it won independence in 2011, South Sudan was divided into 10 states but it has since been subdivided into 32, in what many critics see as gerrymandering of traditional boundaries by Kiir to bolster his power.
Machar is insisting on a return to the original 10 states, or 21 states as based on colonial boundaries.
A technical commission set up under the peace agreement to find a compromise, failed to do so and said only a political agreement would lead to progress.
War broke out in South Sudan in December 2013 after a dispute between Kiir and Machar sparked ethnic clashes and brutal violence, leaving almost 400,000 dead.
Another sticking point has been security issues, such as training and uniting rebel and government troops into a single army and assuring Machar's safety in Juba.