Niger has been a key Western ally in the fight against Islamist militants in West Africa.

The US and France, the former colonial power, both have military bases in the uranium-rich country.

The unverified voice message from Mr Prigozhin appeared on a Telegram app channel associated with the group, saying the takeover was long overdue.

According to the Reuters news agency, the speaker had the same distinctive intonation and turn of phrase in Russian as the Wagner boss.

"What happened in Niger is nothing more than the struggle of the people of Niger against colonisers, who tried to impose their own rules of life," AFP news agency quotes him as saying.

"In order to maintain their actual slave system in the territories of these states, they deploy various foreign missions, which number tens of thousands of soldiers."

He went on to hail the "effectiveness" of Wagner, explaining a thousand of its fighters "are able to restore order and destroy terrorists, preventing them from harming the civilian population", AFP reports.

The release of voice message coincided with the publication on Telegram of photographs showing Mr Prigozhin in St Petersburg at the Africa-Russia summit.

He was seen shaking hands with Ambassador Freddy Mapouka, a senior official in the Central African Republic (CAR).

It is the first confirmed sighting of Mr Prigozhin in Russia since Wagner's failed mutiny in June.

Wagner has a security contract in CAR and through its network of companies allegedly trades there in conflict minerals and timber, as well as making beer and vodka.

The shadowy mercenary group is also in Mali, where it is believed to have about 1,000 soldiers and where its troops have been accused of carrying out atrocities.

Their deployment in December 2021 had followed a breakdown in diplomatic relations between Mali's military regime and France, prompting the former colonial power to withdraw its counter-terror troops.

According to Reuters, the Wagner boss was heard in a video released earlier this month telling his men, now exiled to Belarus, that they should gather their strength for a "new journey to Africa".