Fears have soared in recent days of renewed ethnic slaughter in the Sudanese region of Darfur, where genocidal violence killed as many as 300,000 people two decades ago, with a threatened assault looming over an embattled city already facing famine.

The contest for control of El Fasher, the last city held by Sudan’s military in Darfur, has prompted alarmed warnings from American and United Nations officials who fear mass bloodshed may be imminent. Linda Thomas-Greenfield, the U.S. envoy to the United Nations, told reporters Monday that the city was "on the precipice of a large-scale massacre.”

El Fasher is the latest flashpoint in a year-old civil war between Sudan’s military and the Rapid Support Forces (RSF), a powerful paramilitary group the military once nurtured that is now its bitter rival for power. The conflict has devastated one of Africa’s largest countries and created a vast humanitarian crisis U.N. officials say is one of the biggest in decades.