The scientist who cloned the world's first human embryo yesterday resigned in disgrace from an international body after admitting that he lied about the source of the eggs used in his experiments.
Professor Woo-Suk Hwang of Seoul National University in South Korea apologised for repeatedly denying that some of the eggs had come from junior members of his own research team.
He said he was sorry for making misleading statements when questioned about whether the eggs had been procured unethically from young female colleagues.
Announcing he was stepping down as head of the World Stem Cell Hub "to atone to the public", Professor Hwang appeared downcast and solemn at a press conference yesterday.
"I am very sorry that I have to tell the public words that are too shameful and horrible," he said.
"I should be here reporting the successful results of our research, but I'm sorry instead to have to apologise."
Professor Hwang had been feted around the world when in February 2004 he announced that his team has cloned the first human embryo with a view to developing a new source of stem cells.
However, rumours later emerged that some of the eggs from the 16 volunteer donors came from his colleagues which, although not illegal, is considered unethical because the women have felt under pressure to cooperate.
Professor Hwang also said that no money had changed hands with the donors but it emerged this week that a colleague had in fact paid the equivalent of about £1,000 each to some of the women.
"Being too focused on scientific development, I may not have seen all the ethical issues related to my research," Professor Hwang said.
"At the time, technology was not as advanced as today and creating one stem cell line required oocytes [eggs].
"It was during this time when my researchers suggested making voluntary donations. I clearly turned it down," he said.
But it has now been confirmed that at least two women from his team did donate their eggs, a fact that Professor Hwang claimed he had only become aware of earlier this year.
"The responsibility for all disputes and controversy lies on me. I will not make any excuse," he said.
"It is my way of seeking repentance. I again sincerely apologise for having stirred concern at home and abroad."
Professor Hwang's admission came after an American colleague said that he would no longer work with the South Korean scientist because of allegations about unethical behaviour.
Professor Gerald Schatten of Pittsburgh University School of Medicine in Pennsylvania said in a statement: "Information came to my attention suggesting that misrepresentations might have occurred relating to those oocyte donations."
The two scientists began collaborating in 1984, after Professor Hwang had published his pioneering research in the journal Science which unveiled the first cloned human embryo.
Professor Hwang had always maintained that the eggs used in the 2004 cloning research were obtained ethically from 16 volunteers who had not been paid for the 242 eggs they had donated.
He had also strenuously denied allegations which first surfaced in the journal Nature last year that some of the eggs used in this study came from junior members of his own team.
Donald Kennedy, the editor-in-chief of Science, said that he is taking the allegations very seriously and that he will take "appropriate action" if the allegations are substantiated.
Scientists said that it would not be possible to obtain human eggs in Britain by the unethical methods used by the South Korean team.
"In the UK we are fortunate to have had the Human Fertilisation and Embryology Authority in place for 15 years to supervise all research with human embryos," said Professor Ian Wilmut of the University of Edinburgh, who cloned Dolly the sheep.
Peter Braude, a stem cell scientist at Kings College London, said: "This is an awful shame, that a talented researcher has been found to have lied when questioned on this specific issue over a year ago.
"However it does not detract from the very real advance that the group has made to the science of stem cell therapy in demonstrating that tailor-made lines can be made relatively easily from eggs if they are donated by young women."
"The means to achieving this is questionable, not the data. We must give serious thought to how we can obtain eggs from young women in an ethical way," he added.