Three journalists murdered in the Central African Republic in July were being accompanied by a driver connected to the secretive Russian mercenaries they were investigating, a report has found, calling into doubt Moscow's official explanation that they were shot in a robbery.

The new investigation provides the strongest evidence yet that Orkhan Dzhemal, Alexander Rastorguyev and Kirill Radchenko were killed for trying to report on military contractors whose existence is not admitted by the Kremlin.

The revelations came after the CAR revealed its army's chief of staff trained in Russia, highlighting Moscow's growing military ties with Africa, which have alarmed the West.

The CAR defence minister said during a visit to Russia on Thursday that Moscow was welcome to open a military base in the war-torn republic, where rebel groups still control large areas.

Thursday's findings on the journalists' killing uncovered troubling links with Yevgeny Prigozhin, a catering magnate dubbed “Vladimir Putin's chef” who is known as the patron of the Wagner mercenary group they were investigating.

Prigozhin was sanctioned by the United States in February for financing the troll factory that interfered in the 2016 presidential election to help Donald Trump. Washington sanctioned Wagner in 2017 for fighting alongside Russia-backed separatists in eastern Ukraine.