Russia's mercenary Wagner group has told the family of a Russian fighter captured alive in Mali that he has now died, according to text messages seen by Reuters, contradicting information provided by the Tuareg rebel group that held him.

Alexander Efremov was one of two Russian prisoners captured alive by Tuareg rebels following a deadly desert battle that wiped out dozens of Wagner fighters in late July.

His brother Evgeny said Wagner had called to communicate his death. He posted the news this week on a Telegram chat group used by relatives of the mercenaries who participated in the battle to share information.

"Can you imagine the mental condition of Nike's wife after this call," Evgeny Efremov told the group, referring to his brother by his callsign.

Efremov did not respond to a request for comment. But relatives of three other fighters who had been reported missing told Reuters they had received similar calls from Wagner.

However, a spokesman for the Tuareg rebel group rebuffed Wagner's assertion, telling Reuters that both Russian prisoners, along with Malian army prisoners captured in the same battle, were still alive.

"All our prisoners are alive," said Mohamed Elmaouloud Ramadane, a spokesman for a Tuareg organisation known as the Permanent Strategic Framework for Peace, Security and Development (CSP). "Wagner are liars."

The reason for the contradictory reporting was unclear. The Tuareg group declined to provide evidence that its prisoners were alive, while Wagner has not recovered the bodies of its fighters killed in the battle near the Algerian border, leaving relatives without clear evidence either way.

DESERT BATTLE

Wagner initially reported most of the fighters involved in the desert battle as missing in action. Using public data, facial recognition software and interviews with relatives, Reuters has identified the names of 31 mercenaries either missing or captured following the battle with the Tuaregs.

While Wagner acknowledged heavy losses in the Mali ambush, it has provided no figure on casualties. The Malian army, which fought alongside the Russians, has not given a toll either.

Tuareg separatists, who are fighting for an independent homeland, said they had killed 84 Russians and 47 Malians.

The group launched its insurgency against the Malian government in 2012, demanding an independent homeland called Azawad. Their struggle later became entangled with an al Qaeda-aligned Islamist rebellion in the same region.

The Russian foreign ministry did not respond to a request for comment on the fate of the Wagner fighters.

After the death of the group's leader Yevgeny Prigozhin last year, the Kremlin reeled in Wagner and other mercenary outfits under an umbrella organization now known as Africa Corps.