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 has identified more than 31 km (19 miles) of berms - as the raised banks are known - 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 the army, which has been battling the RSF since April 2023.
The Sudan Doctors Network has told the BBC the RSF is 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 strategy. But the analysis by Yale's HRL suggests that the RSF is creating a literal kill box around el-Fasher.
The HRL report notes that the physical boundary deepens siege conditions and control of who and what can enter or leave the city, where about 300,000 people live.
Since the conflict erupted, RSF fighters and allied Arab militia in Darfur have been accused of targeting people from non-Arab ethnic groups.
Some civilians are trying to escape the city but sadly they are being targeted and killed by the RSF forces, Dr Hassan said.
The RSF has previously denied charges of targeting civilians and ethnic cleansing.
Humanitarian organizations have been unable to access el-Fasher for months and the remaining civilians are enduring constant bombardment, food scarcity, and difficulties in accessing medical care.
With the construction of the physical wall, the HRL report notes that the RSF has also determined the tactical conditions necessary for the defeat of the army division based there.
El-Fasher's fall would mean that the RSF fully controls the western region of Darfur, raising concerns of a potential partitioning of the country as the warring forces have each appointed their own governments.
The RSF continues ongoing construction of the earthen wall, further complicating the situation for civilians seeking to flee or receive essential aid.
According to Yale's HRL, the majority of the village of Alsen has been destroyed, and the vital water treatment facility has sustained damage from RSF bombardments.
Former governor Adeeb Abdel Rahman Youssef has urged the UN Security Council to protect the civilians in el-Fasher, stressing that they are paying the heaviest price amidst the chaos.
