By Charles Scanlon
BBC News, Seoul
A South Korean cloning pioneer has insisted his work meets government ethical standards over human egg donations.
Dr Hwang is hailed as a hero in South Korea
He was speaking after an American colleague ended his collaboration, alleging unacceptable practices to acquire eggs from human donors.
Hwang Woo-suk has been seen as a world leader in the field since he created stem cells using cloned embryos.
The cells are seen as a potential cure for a range of degenerative diseases.
Dr Hwang has been seen as a national hero in South Korea, celebrated by the government and media for his pioneering work.
But confidence in him is being shaken by renewed charges of unethical practices.
It is alleged that some of the human eggs he used were obtained from a junior member of his research team, raising questions about possible coercion.
Loss of trust
A key American collaborator has said he is ending his 20-month association with the Korean team, citing ethical concerns.
Gerald Schatten of Pittsburgh University said he could no longer trust Dr Hwang's denials.
Another research partner was forced to resign last month after it was revealed he had used eggs for fertility treatment which had been illegally purchased from donors.
South Korean scientists have been seen as world leaders after successfully growing stem cells from a cloned human embryo last year.
They say such cells could eventually be used to cure a range of diseases, including diabetes and Alzheimer's.
Last month the team opened a global research hub, intended to produce stem cell lines for use by scientists in other countries.
Dr Hwang has refused to directly address the allegations against him, but he said he was in full compliance