The United Nations Commission on Human Rights in South Sudan has warned that the country is facing an increased risk of mass violence against civilians as renewed clashes grip the country's eastern region.

The commission on Sunday expressed "grave alarm" at fighting in Jonglei state, north of the capital Juba, where witnesses have described civilians fleeing into swamps.

South Sudan People's Defense Force (SSPDF) spokesperson Lul Ruai Koang later on Sunday told Jonglei residents to "immediately evacuate" areas controlled by the Sudan People's Liberation Army-In-Opposition (SPLA-IO) and move to "government-controlled areas as soon as possible."

The two forces have fought several times over the past year, but the most sustained clashes began in late December in Jonglei.

Public statements by commanders encouraging violence against civilians, along with troop mobilization, "represent a dangerous escalation at a moment when the political foundations of the peace process are already severely weakened", the UN commission said.

Meanwhile, the UN mission in South Sudan (UNMISS) has also expressed concern about the public declarations.

"Inflammatory rhetoric calling for violence against civilians, including the most vulnerable, is utterly abhorrent and must stop now," said UNMISS head Graham Maitland.

Renewed fighting in South Sudan has displaced more than 180,000 people, according to the country's authorities.

The UN has urged South Sudanese leaders to prioritize the safety and well-being of civilians, warning that continued escalation could undo years of fragile peace efforts and lead to further humanitarian crises.