South Sudan is in "alarming regression" as clashes in recent weeks in the northeast threaten to undo years of progress towards peace, the UN commission on human rights in the country warned on Saturday.
A fragile power-sharing agreement between President Salva Kiir and First Vice President Riek Machar has been put in peril by the clashes between their allied forces in the country's Upper Nile State.
On Friday, a United Nations helicopter attempting to rescue soldiers in the state was attacked, killing one crew member and wounding two others.
An army general was also killed in the failed rescue mission, the UN Mission in South Sudan (UNMISS) said Friday.
The incident sent shudders through the young and impoverished nation, long plagued by political instability and violence.
Kiir late on Friday urged calm and pledged no return to war.
In a statement on Saturday, the chair of the UN commission, Yasmin Sooka, said South Sudan was "witnessing an alarming regression that could erase years of hard-won progress".
"Rather than fuelling division and conflict, leaders must urgently refocus on the peace process, uphold the human rights of South Sudanese citizens, and ensure a smooth transition to democracy," she said.
South Sudan, the world's youngest country, ended a five-year civil war in 2018 with the power-sharing agreement between bitter rivals Kiir and Machar.
But Kiir's allies have accused Machar's forces of fomenting unrest in Nasir County, in Upper Nile State, in league with the so-called White Army, a loose band of armed youths in the region from the same ethnic Nuer community as the vice-president.
"What we are witnessing now is a return to the reckless power struggles that have devastated the country in the past," commissioner Barney Afako said in the UN Commission statement.
He added that the South Sudanese had endured "atrocities, rights violations which amount to serious crimes, economic mismanagement, and ever worsening security".
"They deserve respite and peace, not another cycle of war."
The African Union (AU) also expressed concern, in a statement on Saturday saying it "strongly condemns this violent escalation" and calling for an "immediate end to the hostilities".