The United Nations called Thursday for urgent action to prevent “large-scale, ethnically-driven attacks and atrocities” in Sudan’s besieged western city of El-Fasher.

The call from the UN rights office came after reports that long-range drones were being pre-positioned by Sudan’s paramilitary Rapid Support forces in South Darfur, raising fears of a large attack on the North Darfur city of El-Fasher in coming days.