South Africa's government says it has received distress calls from 17 citizens who have joined mercenary forces in the Russia-Ukraine conflict.

The men are between the ages of 20 and 39 years and are trapped in Ukraine's war-torn Donbas region.

President Cyril Ramaphosa has "ordered an investigation into the circumstances that led to the recruitment of these young men into these seemingly mercenary activities," a government spokesman said. The statement did not say which side of the conflict the South Africans were fighting for.

Working as a mercenary or fighting on behalf of another government is illegal in South Africa, unless the government authorises it.

The men were lured to join the mercenary forces under the pretext of lucrative contracts, the government said.

Spokesman Vincent Magwenya added the South African government is working through "diplomatic channels" to secure their return.

Magwenya said 16 of the men were from KwaZulu-Natal and one from the Eastern Cape.

"President Ramaphosa and the South African government strongly condemn the exploitation of young vulnerable people by individuals working with foreign military entities," he added.

South Africa has an unemployment rate of more than 30%, and is even higher among young people, making them vulnerable for recruitment, analysts say.

The BBC has found evidence to suggest the Kremlin is working to expand its sphere of influence in Africa.

Africa Corps, a Russian mercenary group controlled by the Russian Ministry of Defence, has effectively replaced the rival military group Wagner in West Africa, after its leader Yevgeny Prigozhin was killed in a plane crash.

In August, the South African government issued a warning to young women not to fall for social media recruitment opportunities promoting jobs abroad, particularly in Russia.

A BBC investigation found young women had been taken to the Alabuga Special Economic Zone in the Republic of Tatarstan in Russia to work in a drones factory.

It is estimated more than 1,000 women have been recruited from across Africa and South Asia to work in Alabuga's weapons factories.

In September, Kenyan police said they had rescued more than 20 people from a suspected trafficking ring that had lured them with job offers in Russia but intended to send them to fight in Ukraine.

Ukraine has previously said that it was holding citizens of various countries - Somalia, Sierra Leone, Togo, Cuba and Sri Lanka - at prisoner-of-war camps.

Ukraine has also previously come in for criticism for trying to recruit foreign nationals, including Africans, to fight on its side.

In 2022, Senegal's foreign ministry said it had summoned Kyiv's ambassador to demand the withdrawal of an embassy post on Facebook urging foreigners to enlist for its war effort.

At the time, Nigeria also warned that it would not tolerate Ukraine's recruitment drive, forcing it to back-pedal.