The South Sudan peace monitoring agency has expressed concern over the military build-up in Yei River State in Central Equatoria.
The Reconstituted Joint Monitoring and Evaluation Commission (RJMEC), has disclosed that it has received several credible reports of military deployment to Yei by both the government and rebels under the command of Gen Thomas Cirillo.
Gen Cirillo is the leader of the National Salvation Front (NAS), which refused to sign the September peace deal.
The peace was signed between President Salva Kiir and former rebel chief Riek Machar in Addis Ababa.
"In response to having received various reports of military build-up in the area of Yei River State, the Reconstituted Joint Monitoring and Evaluation Commission (RJMEC) urges restraint on all sides," the lobby group said in a statement to the media.
RJMEC noted that any military confrontation could derail the implementation of the entire peace deal.
"The progress made so far in terms of the Cessation of Hostilities Agreement (CoHA) of December 2017 and the Revitalised Agreement on the Resolution of the Conflict in the Republic of South Sudan (R-ARCSS) of September 2018 is a worthy achievement and should not in any way be looked on lightly by any party.
"RJMEC wishes to make it clear to all parties that South Sudan is presently at a critical phase of the implementation of the peace agreement, which since signing, has been characterised by a spirit of cooperation," the group said.
"Likewise, that the ceasefire has been largely holding is a great credit to all its signatories, and we urge that this continues. The silencing of guns is a matter of high national importance.
"RJMEC therefore, urges all parties to grasp firmly the Igad-led diplomatic process and allow the full implementation of the peace Agreement," it concluded.
South Sudan army deputy spokesperson declined to answer phone calls seeking his comment on the matter.