Warning: This story contains descriptions of torture and physical violence. Some readers may find it distressing.

A shopkeeper has told the BBC how Russian mercenaries fighting jihadists in Mali carried out the cold-blooded murder of two men in front of him and then threatened to chop off his fingers and kill him too.

This is one of several similar testimonies collected by the BBC showing the tactics used by the Russian fighters as they waged a brutal counter-insurgency operation against Islamist militants in the West African nation - methods widely condemned by human rights groups.

A military junta seized power in Mali in 2021, forcing French troops to leave after accusing them of failing to stem the insurgency. The junta pivoted towards Russia, enlisting the help of the Wagner mercenary group, which was at the time linked to the Kremlin.

Wagner has since pulled out of the country, and its operations have been taken over by Africa Corps, which falls under Russia's defence ministry.

Some of the Wagner mercenaries highlighted their atrocities on an invitation-only Telegram group until it was shut down in the middle of this year, said a report released by the European Council on Foreign Relations last month.

They regularly shared photos and videos of murder, rape, torture, cannibalism and desecration of corpses against alleged insurgents and civilians, the report added.

In June, the Africa Report publication said it had infiltrated the Wagner-linked Telegram channel, finding 322 videos and 647 photographs of atrocities, including severed heads and gouged-out eyes, and posts laced with racism.

The shopkeeper we spoke to has fled Mali and is now living in a refugee camp across the border in Mauritania. We have named him Ahmed, and have changed the names of all the victims quoted in this article for their own safety.

He recounted being subjected to torture while detained by the Wagner combatants, accusing his boss of colluding with jihadists. Ahmed described being underwater tortured and witnessing brutal killings firsthand. After 15 days of imprisonment, Ahmed managed to escape with his wife and children to safety in Mauritania, where thousands of others have found refuge from the ongoing turmoil in Mali.

International observers note the atrocities committed by Russian mercenaries and their impact on local communities, with many survivors suffering physical and psychological scars from their experiences. Reports from the ground indicate a severe humanitarian crisis, with ongoing violence leading to mass displacements and a complete breakdown of law and order in affected regions.