Four staff members at South Africa's flagship Kruger National Park have been arrested on suspicion of killing rhinos and selling their horns to criminal syndicates.
Home to more than 90% of the continent's rhinos, South Africa is on the front line of a worsening war with poachers who send the horns to China and Southeast Asia for use in traditional medicine.
Parks chief David Mabunda said says: "The unscrupulous and revolting hands of the poaching syndicates have stretched as far as to taint the hands of those trusted with the great responsibility of being guardians of our natural heritage."
Poachers killed a record 448 rhinoceroses in South Africa last year and have alredy killed 80 this year.
The government has sent troops to the 19 500 square km Kruger Park, which is home to thousands of the animals, in a bid to reduce the slaughter.
A decade ago South Africa had more than 20 000 rhinos and was losing about 15 a year to poachers.
However poaching has increased dramatically in the last few years as the spread of wealth in places like Vietnam and Thailand has enabled more people to buy powdered rhino horn, a prized ingredient in traditional medicine, though it has no proved benefits.
The street value of rhino horn is higher than that of gold in many parts of Southeast Asia.