More than 70 people have been killed following a drone strike on a mosque in Sudan's Darfur region, a senior medical source has told the BBC.

Friday's attack in the city of el-Fasher has been blamed on the paramilitary Rapid Support Forces (RSF), but the group has not taken responsibility. The RSF and the army have been engaged in a ferocious civil war for more than two years.

The paramilitaries are gaining ground as they fight to seize complete control of el-Fasher - the last army stronghold in Darfur and home to more than 300,000 civilians who have been trapped by the fighting.

One resident told the BBC the drone struck during morning prayers, killing dozens of people instantly. The medical source said 78 died and about 20 were injured, but the process of extracting the bodies from the rubble of the building was still ongoing.

BBC Verify has authenticated footage showing around 30 bodies wrapped in shrouds and blankets next to the mosque, which was located in the west of the city.

This week the RSF launched a renewed offensive on El Fasher, which it has besieged for more than a year. Reports indicate that this included fierce attacks on Abu Shouk, a camp for displaced people near the city.

Satellite images suggest RSF units now control much of the camp, according to Yale University's Humanitarian Research Lab (HRL), which monitors wars. Furthermore, the HRL's assessment indicates that RSF has entered the headquarters of the Joint Forces, a collective of armed groups allied to the Sudanese army, located in a former UN compound.

These developments would threaten el-Fasher's airport and the army division headquarters, putting them within direct RSF firing range. The HRL warns that el-Fasher is likely to fall to the RSF unless the Sudanese military receives immediate reinforcements, marking a significant shift in the ongoing conflict.

Sudan analysts fear that the RSF will target civilians still remaining in the city, many of whom belong to ethnic groups viewed as adversaries by the paramilitary forces. A recent United Nations report outlines the increasing ethnic tensions within the conflict, highlighting that both sides retaliate against individuals suspected of cooperating with opposing factions.

The RSF has faced allegations of ethnic cleansing, particularly against non-Arab communities in areas under their control. The medical charity Doctors Without Borders indicates that RSF troops have expressed intentions to 'clean El Fasher' of its non-Arab population. However, the RSF has denied these accusations, asserting they are unrelated to tribal conflicts.