Africa's rhinos face their worst poaching crisis in decades with organized crime syndicates killing more than 800 in the past three years alone, a global network of conservationists said Friday.

The two horns on each of the plant-eating, poor-sighted African rhinoceros sell like gold on the black market. Each pound can fetch tens of thousands of dollars in southeast Asia where the horns are thought to have medicinal value.

The Swiss-based International Union for Conservation of Nature said poaching of the two different species of African rhinos is on the rise in South Africa, Zimbabwe and Kenya, due to well-equipped and sophisticated crime gangs.

South Africa alone lost 333 rhinos last year and so far this year has lost more than 70, according to IUCN, the world's oldest and largest environmental network. It said most rhino horns leaving Africa are ground into medicine for Asian markets, and Vietnamese are repeatedly implicated in South Africa's poaching trade.

Richard Emslie, a scientific officer with IUCN, said the remaining 24,990 rhinos on the African continent might start to decline again in numbers "unless the rapid escalation in poaching in recent years can be halted."

At last count there were 4,840 black rhinos and 20,150 white rhinos, an improvement from 2007 when there were 4,240 black rhinos and 17,500 white rhinos.

"Although good biological management and anti-poaching efforts have led to modest population gains for both species of African rhino, we are still very concerned about the increasing involvement of organized criminal poaching networks," Emslie said.

The U.N.'s Convention on International Trade in Endangered Species banned the commercial trade in rhino horn in 1993.

But the horns are a key ingredient in Chinese traditional medicine, prized as a cure for everything from colds to impotence. They are made largely of the protein keratin, the same substance as human hair and nails.

Poachers are using helicopters, night-vision goggles and high-powered rifles to hunt and kill rhinos — equipment even African wildlife officials can't afford.