Scientists from Seoul National University in South Korea say they have succeeded in cloning early stage human embryos and growing them in a laboratory. The achievement is sure to revive the debate on human cloning.
The South Korean team says it managed to clone 30 human "blastocysts", or early stage embryos, from eggs donated by 16 South Korean women.
The team says that once the blastocysts began to grow, it successfully removed the versatile "stem cells", which go on to form human organs, and can be used to grow any kind of body tissue.
Members of the team have said their aim was what is called "therapeutic cloning," as opposed to "reproductive cloning." They are interested, in other words, in stem cell research rather than cloning an entire human being.
The team's findings are to appear this week in the online version of the American journal, Science.
The American Association for the Advancement of Science, which publishes the journal, said Thursday that the South Korean biologists are the first to publish successful research on the cloning of human embryonic cells.
Scientists have successfully cloned cattle, mice and, most famous of all, Dolly the Sheep. There have been claims from time to time that human embryos have been cloned, but no proof has ever been offered.
The technique used by the Korean scientists had previously been used to clone mouse cells, but the involvement of human stem cells is likely to reinvigorate the debate on human cloning.
There are many objections to such science. Some people flatly oppose human cloning on ethical and scientific grounds. Others object to the removal of stem cells from cloned human embryos because the embryo is killed in the process.
Supporters of the science argue that stem cell research will lead to innovations in medicine.
Wendy Fung is a researcher at the Hong Kong-based biotech firm DNA Chips.
"Another purpose of this kind of experiment would be to try to find a way to find embryonic tissue that can be used for transplantation," she explained.
Stem cells have been transplanted into diseased organs - like the brain of a person with Alzheimer's or Parkinson's Disease - with beneficial results.
Scientists point out, however, that once human embryos are cloned, they can theoretically be grown into full term humans. A number of individuals and governments have called for laws against the cloning of human beings.
The Bush Administration has been pushing for a ban on human cloning, both for the purpose of reproduction and for extracting stem cells.