The group of more than a dozen independent United Nations experts voiced outrage after the discovery last week of bodies near a Malian military camp days after the army and Russian mercenaries arrested dozens of civilians.

"We urge Malian authorities to conduct prompt, effective, thorough, independent, impartial and transparent investigations into these killings and enforced disappearances," the experts said in a statement.

"Those responsible for unlawful killings and enforced disappearances, whether by direct involvement or complicity, must be prosecuted."

Mali, ruled by a junta following coups in 2020 and 2021, has been grappling with widespread insecurity for more than a decade, largely fuelled by Islamist fighters linked to Al-Qaeda and the Islamic State group.

The country's military rulers have broken their long-standing alliance with former colonial ruler France and turned toward Russia.

The junta enlists the services of what it claims are Russian military instructors, but who -- according to a host of experts and observers -- are mercenaries from the private Russian company Wagner.

In Wednesday's statement, the 13 experts, including the UN special rapporteurs on the rights situation in Mali and on summary executions, stressed that unlawful killings could amount to war crimes.

Enforced disappearances may meanwhile constitute crimes against humanity if they are part of widespread or systematic attacks against civilians, they said.

On April 12, Malian army soldiers and Russian mercenaries arrested dozens of men at a market in Sebabougou, in the country's southwest, and took them to the Kawla military camp, two survivors who fled to Mauritania told AFP.

"According to unconfirmed reports, those arrested were tortured and interrogated about alleged links with 'terrorists' at the Kwala military camp," the expert statement said.

"Afterwards, military and security personnel recruited by the Wagner Group reportedly took the victims out of the camp and executed them."

While the exact death toll remained unclear, at least 65 people reportedly disappeared or went missing after being arrested in Sebabougou.

The independent experts, who are mandated by the UN Human Rights Council but do not speak on behalf of the United Nations, said they had received a list from credible sources purporting to show the names of 54 alleged male victims.

"We are deeply troubled by the apparent total impunity and lack of prosecution or prevention of these violations," the experts said.

"Under international law, military commanders and other superiors, including government officials, can be held criminally responsible for crimes committed by armed forces under their effective command and control."