But the controversial experiment announced on Wednesday is also likely to raise new concerns about cloning human beings, attempts at which have been widely criticised in many countries.

"Because these cells carry the nuclear genome of the individual, after differentiation they could be expected to be transplanted without immune rejection for treatment of degenerative disorders," said doctor Woo Suk Hwang of Seoul National University in Korea, the lead researcher on the project.

"Our approach opens the door for the use of these specially developed cells in transplantation medicine," he pointed out in a statement released by the American Association for the Advancement of Science.

The method has been previously used to generate cells from mice, but up to now, nobody has been successful in applying it to humans, US scientists commented.

The experiment, the first published report of cloned human stem cells, means so-called therapeutic cloning is no longer a theory but a reality.

Supporters of medical cloning say it can transform medicine, offering tailored and highly effective treatments for diseases ranging from Parkinson's to diabetes.

Healing potential

They say it could eventually lead to grow-your-own organ transplants.

Cloned human stem cells could eventually lead to grow-your-own organ transplants.

 



 

The stem cells taken from the tiny embryos, known as blastocysts, have the potential to develop into any kind of cell or tissue in the body.

"Our approach opens the door for the use of these specially developed cells in transplantation medicine," Woo Suk Kwang of Seoul National University in Korea said.

But critics say it involves destroying a human embryo, however tiny, and is thus unethical.

Writing in the journal Science, Hwang and colleagues said they created the clone using eggs and cumulus cells donated by Korean women.

Scientists have cloned sheep, cattle, mice and other species, but have trouble cloning a human being.

Earlier attempt

Last year, a Massachusetts company, Advanced Cell Technology, said it had created a human cloned embryo but it had not grown enough to become a source of stem cells.

The company is still trying but has not reported publicly on its progress.

Stem cells are found throughout the body and are a kind of master cell.

Many scientists believe blastocysts - stem cells taken from days-old embryos - have much greater potential. Each one, when grown correctly, can be directed to become any kind of cell or tissue.