Two separate teams of scientists say they have transformed ordinary human skin cells into ones that look and act like embryonic stem cells.

Laboratory teams at universities in the United States and Japan Tuesday announced the breakthrough, which may someday produce the medical benefits of embryo cloning without political, scientific and ethical controversies.

Both teams used a retrovirus to transport four genes into the skin cells, producing ones that mimic embryonic stem cells.

The landmark research is at the experimental stage. Researchers say the new cells are not ready for use in people because the current technique of producing them requires disrupting DNA of the skin cells, which could potentially cause cancer.

The U.S. team reported its findings in the journal Science, and the Japanese scientists reported theirs in the journal Cell.

Advocates of embryonic stem cell research believe it could aid in the treatment of diabetes, Alzheimer's disease, spinal cord injuries and other diseases. But opponents, including President Bush, say the research is immoral because it involves destroying a potential human life.

Mr. Bush has limited federal funding of stem cell research. Earlier this year, he vetoed legislation that would have eased restrictions on federally funded medical research that uses stem cells as human embryos.

Some information for this report was provided by AFP, AP and Reuters.