WASHINGTON — Scientists at a California company reported yesterday that they had created the first mature cloned human embryos from single skin cells taken from adults, a significant advance toward the goal of growing personalized stem cells for patients suffering from various diseases. Creation of the embryos — grown from cells taken from the company’s chief executive and one of its investors — also offered sobering evidence that few, if any, technical barriers may remain to the creation of cloned babies. That reality could prompt renewed debate on Capitol Hill, where the talk about human cloning has died down of late.

Five of the new embryos grew in laboratory dishes to the stage that fertility doctors consider ready for transfer to a woman’s womb — a degree of development that clones of adult humans have never achieved before.

No one knows if those embryos were healthy enough to grow into babies. But the study leader, who is also the medical director of a fertility clinic, said they looked robust, even as he emphasized that he has no interest in cloning people.

“It’s unethical, and it’s illegal, and we hope no one else does it either,” said Samuel Wood, chief executive of Stemagen in La Jolla, whose skin cells were cloned and who led the study with Andrew French, the firm’s scientific officer. The closely held company hopes to make embryos that are clones, or genetic twins, of patients, then harvest stem cells from those embryos and grow them into replacement tissues. When transplanted into patients, the tissues would not be rejected because the immune system would see them as “self.”

“All our efforts are being directed toward personalized medicine and diseases,” Mr. Wood said, adding that the scientists did not try to extract stem cells from the first embryos they made because they were focused on proving they could make the clones.

Other stem-cell scientists expressed optimism but said they wanted to see the work repeated and more details presented.

“I’d really like to believe it, but I’m not sold yet,” Robert Lanza of Advanced Cell Technology in Worcester, Mass., said. He said the report did not show the results of molecular tests that scientists typically do to prove that the cloning process was complete. And he and George Daley, a stem-cell scientist at Children’s Hospital in Boston, said the embryos look only marginally healthy in photos.

The work is the latest evidence, however, that the field is recovering from the scientific and public relations debacle of 2005, when similar claims by Korean scientists proved to have been fabricated. But opponents of research on human embryos lashed out at the approach.

“This study seems to confirm that human cloning … is technically possible,” Richard Doerflinger of the U.S. Conference of Catholic Bishops said. “It does not show that a viable or normal embryonic stem-cell line can be derived this way, or that any such cell has ‘therapeutic’ value. It does not answer the ethical or social questions about the mass-production of developing human lives in order to destroy them. … It only tells us that these questions are more urgent than ever.”

Other critics noted that scientists in Japan and Wisconsin recently discovered a way to “reprogram” stem cells directly from skin cells, without having to make embryos as a middle step.

“In light of the recent cell reprogramming developments, cloning-based stem-cell research is less justified than ever,” Marcy Darnovsky of the Center for Genetics and Society in Oakland said.

Mr. Wood and others countered that for now, at least, those approaches require the use of gene-altered viruses, which can trigger tumor growth. “It’s hard to believe the FDA would approve the use of those cells,” Mr. Wood said. Criticism also arose on Capitol Hill, where enthusiasm has grown for the newer stem-cell methods that do not involve embryos.

No law bans cloned baby-making, but the Food and Drug Administration has said such experiments would require its approval. Cloning involves fusing an ordinary body cell with a female’s egg cell whose DNA has been removed. Chemical factors inside the egg reprogram the body cell’s DNA so that the newly created cell develops into an embryo that is a genetic twin of the person or animal that donated the body cell.

The technology has developed rapidly in animals, and scientists have been trying to apply it to human cells.