A South Korean scientist, credited with the world's first successful cloning of a human embryo for extraction of stem cells, says it is not scientifically possible to succeed in human cloning.

Seoul National University Professor Hwang Woo-suk made the remarks ahead of a United Nations gathering on human cloning in New York.

Prof. Hwang said he would explain in a keynote speech why human cloning is not possible and the alarming side effects that could result even if scientists were to succeed in human cloning.

The professor said despite the fact that scientific skills on cloning accumulate over a long period of time, the success rate even for animal cloning was still significantly low and that a majority of cloned animals show abnormalities in their key internal organs.