Monitors say unification of about 83,000 security personnel remains far from complete.
South Sudan's ceasefire monitors on Thursday said three weeks had passed without progress made since the parties agreed to extend the pre-transitional period by an additional 100 days to implement security arrangements as stipulated in a September 2018 deal.
Desta Abiche Ageno, chairperson of the ceasefire and transitional security arrangements monitoring and verification mechanism, said unification of about 83,000 security personnel remains far from complete.
He urged the parties to the revitalised agreement to screen and register forces for cantonment in an effort to support the implementation of the 100-day extension.
At a security stakeholders' meeting in Juba, Ageno urged the National Pre-transitional Committee, a national body tasked to oversee the implementation of the peace agreement, to release sufficient resources for cantonment to progress.
"Cantonment is the foundation for the security arrangements and without sufficient resources, the cantonment process will fail," he said.
"The lack of sufficient logistical support to cantonment sites, especially food and medicine, has not been addressed."
President Salva Kiir and ex-rebel leader Riek Machar agreed last month to delay the formation of a unity government by more than three months.
South Sudan descended into civil war in late 2013 and the conflict has created one of the fastest-growing refugee crises in the world, displacing 4 million South Sudanese internally and externally.