Czech authorities said Tuesday they had cracked an international gang smuggling horns of rare white rhinoceroses from South Africa to Asia, where they are prized in traditional medicine.

The gang sent registered Czech game hunters to South Africa to trophy hunt and legally repatriate horns to the Czech Republic. From there, the horns were to be sent on to unspecified Asian countries.

"Sixteen people have been charged, of whom 15 were taken into police custody. They face up to eight years behind bars," according to a Tuesday joint statement by Czech police, customs service and environmental authorities.

Customs officers seized 24 rhino horns, worth an estimated 3.85 million euros ($ 5.1 million).

According to the same statement "each hunter was allowed to kill one rhinoceros at a local game farm" in South Africa. They brought the trophy horns into the European Union using falsified export licences, it said.

"Once back in the Czech Republic the hunters handed the horns over to the organisers of the smuggling operation who then intended to export them to Asia," Ales Hruby, customs service spokesman told reporters in Prague Tuesday.

Native to Southern Africa, white rhinoceroses were thought to be extinct in the late 19th century but around 100 were then discovered in Kwazulu-Natal, South Africa, according to the WWF environmental group.

Classified as "near threatened" there are now an estimated 20,000 animals living in sanctuaries and game parks across the south of Africa.

Limited trophy hunting is permitted under the international Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).