Rhino poaching in South Africa has hit an all-time high with 341 animals killed so far in 2011 – already a bigger death toll than in any previous year.

The total after 10 months surpasses the record total of 333 in the whole of 2010. It confirms a big upward surge in recent years: in 2007, only 13 rhinos were poached.

The animals are being hunted illegally at an average of more than one a day to supply the rhino horn market in the Far East, driven by a belief it can cure cancer.

But while this year's poaching total is set to top 400, South Africa National Parks insisted that the rate is slowing and progress is being made. "It is not so disappointing because it's still below the percentage increase for the past two to three years," said spokeswoman Wanda Mkutshulwa. "Yes, it's looking bad, but it isn't as bad as previous years."

Law enforcement efforts have been stepped up, with more arrests and lengthy prison terms for crimes surrounding poaching and the trade in rhino horns, which are estimated to be worth £35,000 a kilogram. A new programme uses DNA technology to track rhinos and their parts to help catch poachers.

Mkutshulwa added: "We continue to draw on intelligence and security forces. This has gone beyond a conservation issue. This is a criminal issue now. Of course it's not going to be an overnight success, but we believe we will prevail eventually."

South African authorities say they arrested more than 200 suspected rhino poachers between April 2010 and March this year. Sixteen were killed during armed confrontations. Police said on Friday they had detained a Thai man, believed to be an associate of an alleged rhino poaching syndicate "kingpin", at OR Tambo international airport in Johannesburg.

Conservationists have called for more coordinated international efforts. Dr Joseph Okori, WWF's African rhino programme co-ordinator, said: "Vietnam should follow South Africa's example and start sending poachers, traders, smugglers and sellers to jail. In order to save rhinos from extinction, the criminal syndicates operating between South Africa and Vietnam must be uncovered and shut down for good."

The grim milestone in South Africa comes days after the WWF confirmed that rhinos had become extinct in Vietnam, where a small population of Javan rhinos had been hanging on. Failure to conserve the Javan rhinos in Vietnam, where the last individual was found dead with its horn missing and a bullet in its leg, means there is thought to be just one group of fewer than 50 individuals remaining in the world, in Indonesia.

Tom Milliken, rhino programme co-ordinator for Traffic, the wildlife trade monitoring network, said: "It's tragic that the Javan rhino has been wiped out in Vietnam by the same forces that are driving rhino poaching in Africa. This is the ultimate wake-up call for the Vietnamese government to turn aggressively on its internal rhino horn market."

Prince Charles and the Duchess of Cornwall, on tour in South Africa, visited a game reserve on Friday to witness its pioneering efforts to save endangered black rhinos.