South Sudan's President Salva Kiir has been appointed to mediate peace talks between Khartoum and rebels in the Blue Nile, South Kordofan and Darfur conflict zones.
Tut Kew, Kiir's security advisor, told journalists on Monday that the president had agreed "to mediate between the Khartoum government and the armed opposition in Sudan."
South Sudan achieved independence from Sudan in 2011, but the states of Blue Nile and South Kordofan — which both have large ethnic minority populations who fought alongside the south — were left north of the border.
The Sudan People's Liberation Movement-North (SPLM-N), which had been part of Kiir's SPLM, launched an insurgency against Khartoum in the two states that same year.
Juba and Khartoum have traded allegations of supporting each other's rebels on their territory, charges which both countries deny.
Successive rounds of peace talks between Khartoum and the rebels have ended without a deal.
The SPLM-N also has a loose alliance with rebels in Darfur, who have waged an older conflict since 2003 which the UN estimates has killed 300,000 people and displaced more than 2.5 million.
Sudanese officials say the conflict in Darfur has ended, but with media access restricted, reports of fighting there cannot be independently verified.
Kew said Kiir's mediation will involve all rebel groups fighting Khartoum, including those in Blue Nile, Southern Kordofan and Darfur, which all complain of economic and political neglect by President Omar al-Bashir's government.
"Next week mediation will start in Juba where the (Sudanese) opposition delegations and government delegations will begin peace talks," he said.
The SPLM-N has split into two factions, and one of its leaders, Malik Agar, welcomed the move to "unify the SPLM", through his spokesman Mubarak Ardol.
Kiir's mediation comes after Sudan, which is gripped by an economic crisis and is keen to see oil flowing again from South Sudan, has taken an active role in mediating an end to the civil war which broke out in the south in 2013.
Kiir and his rival Riek Machar inked a peace deal in September, which led to Machar returning to Juba for the first time since fleeing in a hail of gunfire in 2016 — albeit for a brief visit — in the latest bid to end that conflict, which has killed an estimated 380,000 people.