A cloning pioneer regarded as a hero in his South Korean homeland has resigned and apologised for using human eggs from his own researchers.
Dr Hwang admitted he had misled the magazine Nature
Professor Hwang Woo-suk was chairman of the World Stem Cell Hub, which opened this month, based in Seoul.
"I am very sorry that I have to tell the public words that are too shameful and horrible," he announced publicly.
International medical standards warn against using eggs from researchers who may be vulnerable to pressure.
However, the health ministry in Seoul insists that he is not guilty of any moral or legal wrongdoing, as the eggs were given voluntarily, without the professor's knowledge, and before South Korea introduced a bioethics law in January.
Dr Hwang, 52, gained worldwide fame after producing the world's first cloned human embryos and stem cells tailored to be used on individuals.
Human cloning science offers the possibility that stem cells harvested from cloned embryos could be used to treat diseases like Parkinson's, diabetes and heart disease.
Dr Hwang's breakthrough was seen as particularly important as the stem cells he created were a perfect match for the patient, which could mean treatments without the risk of the body rejecting them.
However, opponents argue that creating and experimenting with human embryos is unethical.
Paid for eggs
Earlier this month Gerald Schatten, a prominent American colleague of Dr Hwang, broke off their collaboration saying he was concerned by the way the group procured human eggs.
When the medical journal Nature pressed Dr Hwang in 2004 about the origin of the eggs, he denied they had been donated by his own researchers.
At a press conference on Thursday he admitted he had not told the truth.
Dr Hwang said when two women on his team offered their own eggs he turned them down.
Later, the women donated their eggs under false names, without his permission.
When asked about this he investigated, and was told about the provenance of the eggs, but lied to Nature because of a "strong request by the researchers to protect their privacy", he said.
South Korea's health ministry also admitted that other women were paid thousands of dollars for their eggs, though this took place without Dr Hwang's knowledge and before a new law outlawed trading in human eggs.
The professor said he was resigning from all public posts, including his chairmanship of the World Stem Cell Hub, which is designed to produce stem cell lines for disease research worldwide.
"It is my way of seeking repentance," he said.
Dr Hwang led the project that led to the creation of cloned dog Snuppy
He added he would continue his research at Seoul National University.
"I again sincerely apologise for having stirred concern at home and abroad," he said.
"Being too focused on scientific development, I may not have seen all the ethical issues related to my research.
"We needed a lot of ova [eggs] for the research but there were not enough ova around," Dr Hwang said, explaining why standards may have slipped.
The research conducted by his team requires large numbers of human eggs, which are difficult to obtain.
The revelations have shaken fellow scientists.
"We are saddened by the confusion that has arisen in Korea and the distress that has been caused to those concerned," said British professors Ian Wilmut and Christopher Shaw.
There are no international laws governing the use of cells and embryos, but scientists said a tough regulatory climate - like that in force in the UK - could prevent such abuses or misunderstandings.
"The excellent research carried out by Hwang and his team must continue, but in a way that considers the ethics in an appropriate way," said Prof Robin Lovell-Badge of the UK's National Institute for Medical Research.