Spokesman Adrian Lackay said the arrest followed an intensive investigation into the illicit trade in rhino horn internationally.

"The man was arrested at 2pm today [Tuesday] carrying R21,000 in cash that was detained. He is believed to be the fourth suspect in a broad syndicate in the export of rhino horns out of the country," said Lackay.

"Two of the four suspects -- Thai nationals Punpitak Chunchom and Chumlong Lemthongthai are still in police custody but Free State game farm owner Marnus Steyl is out on bail."

The man is expected to be formally charged on Wednesday when he appeared in the Kempton Park Magistrate's Court, said Lackay.

Lemthongthai, Chunchom and Steyl were arrested last year.

Steyl was granted R100,000 bail ahead of the trial in June. Chunchom and Lemthongthai remain in custody in separate prisons.

Steyl's farm was allegedly used by a syndicate to hunt rhinos, with Thai prostitutes and strippers posing as bogus rhino hunters.

Once the rhino was shot, the women would then be called to come and pose for photos with the carcasses.

Lemthingthai's company, Xaysavang Trading Export Import, is being charged R65,000 per kilogram of rhino horns.

A South African court found Chunchom guilty last year of smuggling animal products like lion bones into the country. He was fined R10,000.

Both he and Lemthongthai face charges of contravening the Customs and Excise Act, and fraud, according to the report.

It was believed 26 rhinos may have been shot by the syndicate using legal hunting permits.