South Africa's government said on Thursday that it had received distress calls from 17 citizens who had 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," South Africa's government said in a statement.

By law, it is illegal for South African citizens and entities to offer or provide military assistance to foreign governments or to participate in the armies of foreign governments unless authorised by the government, South African public broadcaster SABC reports.

President Ramaphosa said the government was working through diplomatic channels to secure the return of the young men following their calls for assistance to return home, the broadcaster adds.

He also condemned the exploitation of young, vulnerable people by individuals working with foreign military entities.

The Russia-Ukraine war started in February 2022.