Poachers have killed nearly 200 rhinoceros in South Africa so far this year, a huge increase in the number of deaths as criminal gangs increasingly use automatic weapons and helicopters to hunt down their prey.
The World Wide Fund for Nature said Kruger National Park was the site of most of the 193 rhino killings in 2011, and warned that unless more was done, South Africa would lose far more of the animals this year than the record 333 rhinos killed last year. In 2007, just 13 cases were reported.
South Africa has stepped up legal efforts against the poachers, according to WWF, with 123 arrests and six convictions this year, but criminals are increasingly organised.
Dr Joseph Okori, WWF's African rhino programme co-ordinator, said: "Poaching is being undertaken almost without exception by sophisticated criminals, sometimes hunting from helicopters and using automatic weapons.
"South Africa is fighting a war that risks reversing the outstanding conservation gains it made over the past century."
The country has drawn international praise for its rhino conservation effort, bringing the species back from the brink of extinction. It now has about 19,400 white rhinos and 1,678 of the critically endangered black rhinos. But its success has attracted the poachers.
Rhino horn is highly prized in Asia where it is used in traditional medicine and can sell for as much as £36,000 a kilogram on the black market.