The deal, signed in September 2018 in a bid to end almost six years of conflict, has suffered heavy delays.

One of its biggest hurdles has been the logistics of creating so-called cantonment sites, where troops and rebels are screened, trained and integrated into a single force.

The Joint Defense Board (JDB), comprising military commanders from the army and rebel forces, told a press briefing on Friday it had secured food and other essentials to begin the programme.

"JDB today made a very big decision," rebel SPLA-IO spokesman Col. Lam Paul Gabriel told the media in Juba.

"Today they have made it very clear that forces by tomorrow should report to cantonment sites immediately." The forces have been told to report by July 30.

The government's military spokesman Major General Lul Ruai Koang said all the government forces were also ordered to report to their barracks.

The warring parties were supposed to assemble and train their forces together within eight months of the signing of the deal.

But this failed to happen and a six-month extension was agreed in May.

More than 20 cantonment sites have been selected across the country, but forces have complained there is insufficient food, shelter and medicine for them to move there.

South Sudan's war broke out in 2013, two years after independence, after President Salva Kiir accused his former deputy Riek Machar of plotting a coup against him.

The fighting has left 380,000 people dead and forced more than four million South Sudanese -- almost a third of the population -- to flee their homes. Numerous attempts at peace have failed.

Under the terms of the agreement, Machar is to return from exile to serve as vice president in a power-sharing government which must now be in place by November.