The UN called on Saturday for immediate action to stop "wanton killings" of people fleeing El Geneina, the capital of West Darfur state in Sudan, by Arab militias aided by paramilitary forces.
For more than two months, the Sudanese army, headed by Abdel Fattah Al Burhan, has been locked in fighting with the paramilitary Rapid Support Forces commanded by his former deputy Gen Mohamed Dagalo, better known by his nickname Hemedti.
The deadliest violence has raged in Darfur, a vast western region on the border with Chad where the UN has warned the conflict has taken an "ethnic dimension".
"We are gravely concerned that such wanton killings are continuing and urge immediate action to halt them," UN rights office spokeswoman Ravina Shamdasani said in a statement.
"People fleeing El Geneina must be guaranteed safe passage and humanitarian agencies allowed to access to the area to collect the remains of those killed."
The Geneva-based UN rights office said people who escaped to Chad had given "horrifying accounts of armed 'Arab' militia backed by the Rapid Support Forces killing people fleeing El Geneina on foot".
It said witnesses had given "corroborating accounts" of Arab militia targeting men from the non-Arab Masalit people.
"All those interviewed also spoke of seeing dead bodies scattered along the road -- and the stench of decomposition," it said.
"Several people spoke off seeing dozens of bodies in an area referred to as Shukri" about 10 kilometres (six miles) from Sudan's border with Chad.
The UN rights office said that all but two of the 16 people it interviewed testified that they had witnessed "summary executions" and the targeting of civilians on the road from El Geneina to the border between June 15 and 16.
The United States said last week that up to 1,100 people had been killed in El Geneina, in a statement that attributed the atrocities "primarily" to the RSF paramilitary force.
In its statement, the UN rights office said El Geneina had become "uninhabitable", and that essential infrastructure had been destroyed and movement of aid to the city remained blocked.
It called on the RSF leadership to "immediately, unequivocally condemn and stop the killing of people fleeing El Geneina.
"Those responsible for the killings and other violence must be held accountable," it said.
"We urge the immediate establishment of a humanitarian corridor between Chad and El Geneina, and safe passage for civilians out of areas affected by the hostilities."
