The number of rhinos poached in South Africa has risen sharply this year, with more than 400 killed.

South African National Parks says 405 rhinos have been killed for their horns so far in 2011 - 229 in the giant Kruger National Park alone - representing a 22 per cent increase on the 2010 figure.

Arrests of poachers have risen 27 per cent to 210.

South Africa is home to 90 per cent of Africa's white rhino population and the government has banned hunting the animal and the sale of its products in an attempt to stop poaching, but with little success.

Criminal gangs smuggle rhino horns into Asia, where they are sold on the black market as medicine and aphrodisiacs.

The Kruger National Park is one of the biggest in the world, and roughly the size of Israel.

It is also part of a Great Transfrontier Park that links reserves along South Africa's borders with Zimbabwe and Mozambique, through which poachers can enter and leave with ease.

Rhino horn has been used for centuries in Chinese medicine, where it was ground into a powder and often mixed with hot water to treat maladies including rheumatism, gout, high fever and even possession by the devil.

In recent years, it has taken on the reputation for being an aphrodisiac and gained in popularity among the newly rich in Vietnam and other south-east Asian states, where it is seen as a cancer remedy.

This has caused the price of rhino horn to rise to nearly $57,000 a kilogram, making it far more expensive than gold, according to the International Rhino Foundation.

Reuters