The U.N. is calling for safe passage of civilians fleeing paramilitary forces in Darfur and for protection of those remaining in el-Fasher.

Sudanese fleeing a paramilitary force that seized a city in the country’s Darfur region trickled into a nearby refugee camp Thursday after walking for miles, telling aid workers that roads were littered with bodies. Aid groups feared for the fate of thousands more trying to escape, with hundreds reportedly killed in the turmoil.

The RSF had been besieging el-Fasher, the last military-held stronghold in the Darfur region, for the past 500 days.

Its capture raises fears that Africa’s third-largest nation may split, with the paramilitaries holding Darfur and the military holding the capital Khartoum and the north and east of the country.

The U.N. migration agency said over 36,000 have reportedly fled el-Fasher since Sunday, with people fleeing on foot in the middle of the night.

Experts analyzing satellite imagery say an earthen wall built by the RSF around the city is preventing residents from fleeing and has become a “kill box” where some appear to have been shot.

Only thousands have arrived at Tawila, a town some 60 kilometers (35 miles) west of el-Fasher.

Tawila has already burgeoned into a sprawling refugee camp housing hundreds of thousands who fled the RSF’s siege of el-Fasher over the past year.

The World Health Organization warns that 460 people have been killed in a hospital in el-Fasher.

Witnesses report RSF fighters attacking civilians.

The RSF on Thursday denied carrying out killings at the hospital. It said it had arrested a number of individuals accused of committing violations during the seizure of el-Fasher.

Disrupted communications make assessing the devastation difficult.

The International Rescue Committee and the Norwegian Refugee Council both warn of grave danger for those in and around el-Fasher.