A commander in a Russian mercenary group has been killed in Mali following an attack by rebel fighters during a sandstorm, the group said.
The military regime in the West African state had turned to the notorious Wagner group in 2021, seeking support in fighting jihadist and separatist forces.
On Monday the Russian outfit - which has now morphed into a group named Africa Corps - said it had joined Mali's military in "fierce battles" against separatist rebels and jihadist militants last week.
However, the separatists launched a major attack, killing an estimated 20 to 50 mercenaries, sources close to Africa Corps told the BBC.
Similarly, several Russian military bloggers reported that at least 20 were killed in the ambush near the north-eastern town of Tinzaouaten.
In an official statement posted to Telegram, the Russian mercenary group did not specify how many of their troops had died, but they confirmed suffering "losses". This included a commander, Sergei Shevchenko, who was killed in action.
The mercenaries initially "destroyed most of the Islamists and put the rest to flight", the statement said.
"However, [an] ensuing sandstorm allowed the radicals to regroup and increase their numbers to 1,000 people," it added.
The Permanent Strategic Framework for Peace, Security and Development (CSP-PSD), a separatist group dominated by the Tuareg ethnic group, claimed responsibility for the attack.
"On Saturday, our forces dealt a decisive blow to the enemy columns," AFP quoted the CSP-PSD's spokesperson as saying.
Prisoners were taken and "a large amount of equipment and weapons were damaged or captured", the spokesman added.
The rebel group has shared video footage which shows numerous white men in military fatigues lying motionless on a sandy plain.
Another shows a group of mostly black men wearing blindfolds with their hands tied behind their backs.
The BBC has not been able to confirm the authenticity of the videos.
Jamaat Nusrat al-Islam wal-Muslimin (JNIM), an al-Qaeda affiliate, has also claimed sole responsibility for the attack.
The Islamist militants said they killed 50 Russian mercenaries in a "complex ambush".
More than a decade ago, Mali's central government lost control of much of the north following a Tuareg rebellion, which was sparked by a demand for a separate state.
The country's security then was then further complicated by the involvement of Islamist militants in the conflict.
When seizing power in coups in 2020 and 2021, the military cited the government's inability to tackle this unrest.
The new junta severed Mali's long-running alliance with former colonial power France in favour of Russia in a bid to quell the unrest.
But the Wagner mercenary group was in effect dismantled after a mutiny by its leader Yevgeny Prigozhin last year, leading to its replacement in West Africa by Africa Corps.