Wagner has been active in conflicts in Syria and Ukraine, and has sent mercenaries to the Central African Republic and Sudan, according to Western and independent Russian media reports as well as foreign governments.

Journalists Kirill Radchenko, Alexander Rastorguyev and Orkhan Dzhemal had flown to the strife-torn African country to report on Wagner's operations, according to the media organisation they were working with.

Analysts say Moscow uses the private group so it can play down military activity in active conflicts and discount casualties.

Moscow-based defence analyst Pavel Felgenhauer told AFP that Wagner most likely viewed its operations in the Central African Republic as a business opportunity, rather than part of a wider military venture.

"We can assume the Kremlin gave the green light to Wagner's activities in the CAR when the leadership of the country was visiting Russia (in May this year)," he said.

"Without the approval of the Kremlin, Wagner would not be there."

He said mercenaries in Africa would be paid significantly more than those involved in the conflict in eastern Ukraine, making it a more attractive prospect for potential recruits.

The apparent work of the group in the CAR runs in parallel with Russia's official role there. In December it was authorised by the UN to provide the armed forces with weapons and training.

- Troll factory -

Wagner was set up by former Russian intelligence officer Dmitry Utkin, who was part of the first convoy of mercenaries sent to Syria in 2013 -- long before Moscow's official involvement in the conflict.

The group is funded by an ally of President Vladimir Putin, Yevgeny Prigozhin, according to Western and Russian media.

Prigozhin is a Saint Petersburg businessman who made a fortune in catering before signing lucrative contracts with Russia's military and government.

He has also been charged by a US court with setting up an internet "troll factory" that attempted to influence the 2016 American presidential elections in favour of Donald Trump.

Wagner's activity in Syria attracted attention in February after the deaths of several of its employees there.

Various media outlets reported up to 200 fatalities in a US attack on pro-regime troops in Deir ez-Zor.

The Conflict Intelligence Team -- a group of Russian investigative bloggers -- established that dozens of those were members of the Wagner group.

After days of silence, Moscow acknowledged five Russian nationals were killed and dozens were wounded in the attack, saying they were in the country "on their own initiative".

- 'Heroes of the Fatherland' -

The response was similar to Moscow's official line on eastern Ukraine, where a conflict between the Ukrainian army and pro-Russian separatists has left more than 10,000 dead since 2014.

Founder Utkin and the Wagner Group were blacklisted by the US Treasury in 2016 for having "recruited and sent soldiers to fight alongside separatists in eastern Ukraine".

Utkin himself joined the ranks of separatist forces there in the first year of the conflict, following his ill-equipped mission to Syria.

The Kremlin has continuously rejected accusations from Kiev and the West of its military presence in the region, insisting that Russians who are fighting there are "volunteers".

In 2016, Utkin attended a televised ceremony held in the Kremlin to honour "the Heroes of the Fatherland" and was photographed alongside Putin.

Investigating Wagner has already proved a dangerous activity for reporters.

A journalist who was looking into the group's activities in Syria died in April after falling from the balcony of his fifth-floor flat in the Russian city of Yekaterinburg.

Analyst Felgenhauer said he thought it was unlikely the journalists in the Central African Republic were killed by members of the Wagner Group.

"But it is a good advertisement for them. Perhaps some other African leader will hear about Wagner because of this killing and will want some Russian mercenaries for himself," he told AFP.