A human embryo has been successfully cloned for the first time in history, according to an American biotech company.

Advanced Cell Technology, a Worcester, Mass.-based company, announced the results of its unprecedented experiment on Sunday.

The purpose behind the ACT study, which was published in the Nov. 25 issue of the Journal of Regenerative Medicine, was stem cell research, not human cloning.

"These are exciting preliminary results," study co-author Robert P. Lanza, M.D., said in a statement. "Our intention is not to create cloned human beings, but rather to make life-saving therapies for a wide range of human disease conditions."

ACT said that, for the first time ever, it had cloned an embryo to create a cluster of cells that could be used as a source of stem cells, which can in turn form other cells or tissues in the human body.

Stem cell technology can be used to treat diseases such as diabetes, cancer, AIDS, and neurodegenerative disorders like Parkinson's and Alzheimer's.

A spokeswoman for President Bush said he stood by his anti-cloning position.

"The president made it very clear he's opposed to any type of human cloning, and that includes human embryos," said White House spokeswoman Jennifer Millerwise.

Earlier this year, Bush passed a bill prohibiting federal funds from being used in human embryo cloning.

ACT is a private company, but Millerwise said Bush backs a House bill making human cloning a criminal offense.

Several states, including California, have banned human cloning. Congress is considering such a ban.

On Fox News Sunday, Senate Majority Leader Tom Daschle, D-S.D., said that while he does support human cloning for research, he is strongly against cloning for the sole purpose of human replication.

"I don't think there's any need to do that," Daschle said.

Though he said he wanted to wait until he'd had the chance to examine the ACT study before fully reacting, Daschle said he found it unsettling.

"It's disconcerting, frankly," he said. "I think it's going in the wrong direction."

The company's goal in cloning for human medical research is to create stem cells able to grow into a variety of other replacement cells, like those in the heart, blood or neurons. ACT scientists say they have no interest at present in transplanting such early embryos into a woman's womb to give birth to a cloned human being.

"Human therapeutic cloning could be used for a host of age-related diseases," said ACT CEO Michael D. West, Ph.D., another author of the paper. "If the human cells behave as animal cells have in previous studies, we may have found a means of rebuilding the lifespan of cells at the same time."

In findings published Sunday by the Journal of Regenerative Medicine and described online in Scientific American, the scientists said they had grown a six-cell human embryo.

They said they created the early embryo by injecting a very small cell with its genetic material into a woman's donated egg. In such cloning, the injected DNA often comes from a skin cell, but the researchers this time used a cumulus cell, which nurtures a developing egg.

In a separate experiment, the scientists showed they could push the development of human egg cells even further with a technique known as parthenogenesis.

They exposed 22 egg cells to chemicals that changed the concentration of electrically charged ions within them. Six eggs reprogrammed themselves to develop into early embryos known as blastocysts, which contain dozens of cells.

The scientists described the work as preliminary. Neither experiment has yet produced the coveted stems cells that grow inside an embryo and differentiate into other body tissues.

But the researchers described the work as an important step toward producing these stem cells to generate replacement cells as treatments for diabetes, heart disease, spinal injuries, and many other ailments.

ACT researchers collaborated with scientists from Duncan Holly Biomedical of Somerville, Massachusetts on the paper.

The Associated Press contributed to this report.