An extensive earthen wall is being built around the besieged Sudanese city of el-Fasher and is intended to trap people inside, according to research from Yale University.
From satellite images, the university's Humanitarian Research Lab (HRL) has identified more than 31km (19 miles) of berms - or raised banks - constructed since May in territory outside the city occupied by the paramilitary Rapid Support Forces (RSF).
El-Fasher, under siege for more than a year, is the last major foothold in Darfur for Sudan's army, which has been battling the RSF since April 2023.
The Sudan Doctors Network has told the BBC that the RSF was intensifying its offensive there and deliberately targeting civilians.
Yesterday there was a shelling in a civilian area down in the city centre that ended up killing almost 24 civilians and injuring 55 people, among them five women, Dr Mohamed Faisal Hassan, from the medics association, told the BBC's Newsday programme.
The attacks on the central market and a residential area were 'deliberate' and 'heinous', he said.
BBC Verify says both sides in the conflict have been using berms as a defensive tool. But the analysis by Yale's Humanitarian Research Lab indicates that the RSF is creating a literal kill box around el-Fasher.
Since the conflict erupted, RSF fighters and allied Arab militia in Darfur have been accused of targeting people from non-Arab ethnic groups. Civilians attempting to escape the city face significant hazards and attack.
The recent construction of the physical wall has complicated the already dire situation in el-Fasher, where humanitarian organizations have been unable to provide assistance for months. Civilians are enduring persistent bombardment, food scarcity, and lack of medical care, turning the city into a seemingly inescapable fortress amidst ongoing conflict.
Pressure is mounting on the international community, with calls for protection of the civilian population in el-Fasher, which continues to bear the brunt of the chaotic and violent situation unfolding across Sudan.