The Russian security firm, Wagner, said on Sunday that hundreds of its fighters had arrived in the Central African Republic (CAR), according to a statement on the messaging app, Telegram.
At least 1,000 of the mercenaries have been based there since 2018.
There's been uncertainty over the future of Wagner following its short-lived mutiny in June.
Recent reports say about 600 mercenaries had left CAR.
A company linked to the Wagner group said the new arrivals would help provide security during a referendum in the CAR later this month, which will determine whether President Faustin-Archange Touadéra can seek a third term in office.