The group had been spearheading Russian attacks in parts of Ukraine before appearing to turn on the Kremlin after falling out with the Russian military over the conduct of the war.

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Warning: The story below contains references to torture techniques

Washington based anti-corruption organisation The Sentry has found that Yevgeny Prigozhin's mercenary group has been "perfecting a nightmarish blueprint for state capture" in the CAR to enable it to plunder the country's national resources, particularly gold and diamonds.

Over the past five years, soldiers and militiamen have reportedly undergone Wagner training that has involved "ultraviolent" techniques of torture and killing, including how to cut fingers and legs, remove nails, strangle, throw fuel and burn people alive.

In close cooperation with CAR President Faustin-Archange Touadéra, the Wagner Group has significant control over the nation's political and military leadership, as well as huge sway over its economy.

The report also found that part of Wagner's training involved "sweeping" or "cleansing" which sources in the Central African military said meant killing everyone, including women and children.

One military source explained: "We kill villagers only, we bury them, or we throw them in the bush."

A member of the presidential guard discussing the training he received said: "It was a Russian instructor who gave the training … it included commando training, interrogation, aggressive techniques, torture, violence."

The training can last anywhere between one and six months and involves firearms training, hand-to-hand combat, and espionage, interrogation, and torture techniques, according to the report.

Taking advantage of President Touadera's ever-increasing need for security and protection, Wagner has tightened its grip on the CAR's economic resources and constructed a transnational network of shadowy companies and operations stretching from Madagascar, Cameroon, and Sudan all the way back to Moscow.

While Wagner commanders and President Touadéra have justified the group's presence as a means to hunt down armed rebel groups to protect the regime, The Sentry found that Wagner has taken command and control of government armed forces.

It has then gone on to order them to execute "cleansing" campaigns to massacre entire communities that might get in the way of the group's extraction operations.

Soldiers involved in these activities said that Wagner's intention is to create terror and instil fear, not only among rebels but across the population at large and even among the soldiers and militiamen under its control.

When the group first arrived in early 2018, the CAR had undergone decades of deadly crises that the UN and Western countries had failed to adequately address.

Wagner took advantage of this and has, in just few years and with relatively few personnel, become one of the most powerful forces in the CAR.

Its activities in the CAR are just one aspect of the private army's operations on the continent, which span numerous countries across Africa including Libya, Sudan, Mali, Mozambique, Madagascar, and Burkina Faso.

Further afield they are also known to have an extensive presence in Syria.

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Mining companies affiliated with Wagner, primarily Lobaye Invest, Midas Ressources, and Diamville, have been granted mining licences and export authorisations, allowing the group to use its transnational networks across Africa to help set up industrial-scale gold production, according to the report.

It is also believed that Russia delivered heavy military equipment that had not previously appeared in the CAR conflict, including combat helicopters, aircraft, ground vehicles, reconnaissance drones, and heavy weapons including 14.5 mm heavy machine guns.

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The report even alleges that Wagner has been using landmines in CAR.

The UN Panel of Experts on CAR noted that "deliveries of materiel in support of state security forces were observed at a pace unprecedented since the establishment of the arms embargo in 2013."

Nathalia Dukhan, Senior Investigator and head of the Wagner programme at The Sentry, said: "The Central African Republic has become Wagner Group's laboratory of terror.

"With a limited number of military personnel and the active support of President Touadéra, Wagner has managed in just five years to infiltrate and control CAR's military chain of command, as well as the country's political and economic systems.

"Russia has revealed its plan for psychological warfare and domination - a truly new kind of ultraviolent colonialism.

"Without urgent and coordinated global action to counter this threat, Wagner's predatory terrorist network will continue to spread and sow devastation wherever it takes root."

The report urges the US, UK, EU, Canada, Japan and other nations and jurisdictions to widen the scope of sanctions against the group and declare Wagner a terrorist organisation.

The Sentry is an investigative and policy organisation that says it seeks to "disable multinational predatory networks that benefit from violent conflict, repression, and kleptocracy".