President Salva Kiir and his rival, Vice President Riek Machar, agreed on the creation of a unified armed forces command, one of several crucial unresolved issues holding up implementation of the 2018 deal to end the country's bloody five-year civil war.

"Peace is about security and today we have (achieved) a milestone," said Martin Abucha, who signed the agreement on behalf of Machar's opposition party the SPLM/A-IO.

"This to inform everyone that we are for peace and let all of us work for peace," added Kiir's security adviser Tut Gatluak.

Tensions between forces loyal to Kiir and former rebel leader Machar have spiralled recently, triggering fears in the international community of a return to full-blown conflict in the world's youngest nation.

Both men were present at the ceremony in the capital Juba for the signing of the accord, which stipulates a 60-40 distribution of key leadership posts in the army, police and national security forces.

Mohamed Hamdan Daglo, currently the number two in Sudan's post-coup ruling council, had arrived in Juba on Friday on a bid to break the deadlock over the security arrangements.

Sudan drew up the proposal after Kiir on March 25 issued a presidential decree on the formation of the command structure, a move that had been swiftly rejected by Machar as a "unilateral" action.