The South Korean scientist who led the world of stem cell research after claiming a string of extraordinary advances in human cloning has withdrawn one of his key findings because his data contained mistakes.

At a news conference this morning, Dr Hwang Woo-suk, a national hero in South Korea, said he had asked the journal Science to retract an article he wrote in May, in which claimed to have produced 11 colonies of stem cells tailored for specific patients.

Dr Hwang's development of embryonic stem cells that matched the DNA of the patient that would receive them was hailed around the world as a technical triumph and a possible treatment for Parkinson’s disease and diabetes.

His decision to withdraw the article, under pressure from his former research partner, who said yesterday that the work was riddled with fabrications, shocked South Korea and sent stocks in the country's biotechnology companies tumbling.

Last month, Dr Hwang revealed that some of the human eggs used in his research came from his researchers, a breach of ethics that was criticised by colleagues. Today's news is likely to cast doubt over his entire career.

Dr Hwang said today he was withdrawing the article because of problems with its accompanying photographs, and apologised for "fatal errors and loopholes in reporting the scientific accomplishment", but he defended the bulk of his research.

Speaking to journalists after spending a week in hospital recovering from stress, Dr Hwang insisted that the 11 colonies of cells were genuine and that he would produce proof of their existence within ten days: ''We retain our original core technology. We found out later that our management had been poor and as the head of research I feel a grave responsibility," he said.

Dr Hwang's work has been under intense scrutiny since last month, when an American collaborator, Dr Gerald Schatten of the University of Pittsburgh, ended his relationship with the scientist's World Stem Cell Hub citing ''ethical violations'' over the procuring of eggs.

According to The New York Times, Dr Schatten then wrote to Science this week, asking that his name be removed from Dr Hwang's article, which he co-authored earlier this year without witnessing the experimental work that produced the stem cells. Dr Schatten wrote that he had ''substantial doubts about the paper's accuracy'' and had heard that some of the experiments had been fabricated.

Yesterday, Dr Hwang's former research partner, Dr Roh Sung-il made the most damaging accusations yet, telling Korean television: "Hwang today made statements totally contrary to what we have believed is right," adding: "Nine of the 11 stem-cell lines he had said he created didn't even exist."

Responding to Dr Hwang's statement today that he would produce what remained of the stem cell colonies - it is unclear whether some have died or been destroyed by a fungus - Dr Roh said once again that his former partner was lying.

"He’s avoiding taking the responsibility that he should take," Dr Roh told a separate news conference in Seoul. Dr Roh also said that Dr Hwang would be unable to display cell colonies, because he had told him they had all died. "What can I say if Hwang changes the remarks he made with his own mouth yesterday?"

Dr Hwang became one of the world's best-known scientists in February 2004 when his laboratory claimed to have produced the world's first cloned human embryo.

His subsequent claim to have developed patient-specific stem cells - by grafting nuclei from donated eggs to skin cells from patients who needed treatment - was celebrated by fellow scientists as a staggering achievement, albeit with fears of the ethical quandaries that the discovery would raise.

Earlier this year, Dr Hwang, a biologist who said he became fascinated by cloning because he wanted to make healthier cows, added to his fame by creating Snuppy, the world's first cloned dog. Dogs are seen as one of the hardest animals to clone.

Dr Hwang's research and the relative lack of bureaucracy surrounding scientific testing in South Korea has made the country a centre for innovative stem cell research. The government has given Dr Hwang 25 billion won (£14 million) to pursue his work and commissioned stamps in his honour, showing a man rising from a wheelchair to walk.

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