JOHANNESBURG (AFP) - The number of rhinos killed by poachers in South Africa continued to climb this year, with demand for rhino horn in Asia pushing the slaughter ever higher, the government said Sunday.

As of August 27, the number of rhinos lost to poachers was 749 for the whole country, said Environment Minister Edna Molewa. "Of these, 544 were poached in the Kruger National Park. By last year this time the number of rhinos lost to poachers were 716 for the whole of the country and 459 for the KNP."

South Africa's rhinos have been under siege for years. The horn is worth as much as gold in Asian markets, because of its perceived medicinal properties.

It is composed mainly of keratin, the same component as in human nails.

There was some good news on the anti-poaching front however, with Molewa reporting that 138 poachers had been arrested in Kruger National Park this year, up from 81 in the same period in 2014.

"The poaching figures are not cause for despondency," she said. "Were it not for the interventions I have outlined, they could unfortunately be far worse.

"Of course we have to do far more if we are to stop the slaughter of these animals."

Rangers in Kruger park have notably been equipped with infra-red binoculars to try and catch the poachers who operate at night.

Over the past eight years, the number of rhinos killed has reached new records annually.

According to official figures, 1,215 of the animals were slaughtered in 2014 compared to 1,004 in 2013, 668 in 2012, 448 in 2011, 333 in 2010, 122 in 2009, 83 in 2008 and just 13 in 2007.

Some experts believe the real figures are even higher as some of the carcasses are never recovered.

Only some 20,000 rhinos remain in South Africa, about 80 percent of the world total.