The United Nations Mission in South Sudan (UNMISS) is now warning of a possible return to civil war following the arrest of First Vice President Riek Machar.
In a statement, the Head of UNMISS, Nicholas Haysom, also called for immediate recommitment to peace between the warring factions.
He insisted that while the leaders committed to a revitalised peace agreement, any changes to it by any party will only take the country backward.
The Special Representative of the Secretary-General and Head of UNMISS also said that such a move will also destabilise not only South Sudan but the entire region.
"Tonight, the country's leaders stand on the brink of relapsing into widespread conflict or taking the country forward towards peace, recovery and democracy in the spirit of the consensus that was reached in 2018 when they signed and committed to implementing a Revitalized Peace Agreement.
"Unilateral amendments by Parties to that agreement that jeopardize the hard-won gains of the past seven years risk returning the country back into a state of war. This will not only devastate South Sudan but also affect the entire region," Haysom said.
The mission urged all parties to immediately cease hostilities and engage in constructive dialogue.
Haysom said that they must put the best interests of their people at the forefront of the dialogue.
Dr Machar and his wife, Angelina Teny, were placed under house arrest on Wednesday night, an action that now threatens peace in the fragile nation.
Local media say the arrest follows weeks of escalating clashes between Machar's forces and the South Sudan People's Defence Forces near the capital Juba
