The first claim of human-embryo cloning has the criticism multiplying like cloned sheep.

Researchers at Advanced Cell Technology in Worcester, Mass., said Sunday that they had succeeded in cloning human embryos, but that their plan is to develop genetically compatible replacement cells for patients with a range of illnesses — not to eventually clone human beings themselves, as critics charge.

"This work sets the stage for human therapeutic cloning as a potentially limitless source of immune-compatible cells for tissue engineering and transplantation medicine," said Dr. Robert P. Lanza, one of the researchers at the biotechnology company.

But critics of cloning, including President Bush, wasted little time attacking the announcement.

"We should not, as a society, grow life to destroy it," Bush told reporters during a Rose Garden appearance Monday. He said the reported breakthrough was "morally wrong, in my opinion."

The Washington, D.C.-based National Right to Life Committee also criticized the announcement.

"This corporation is creating human embryos for the sole purpose of killing them and harvesting their cells," the group's legislative director, Douglas Johnson, said on Sunday. "Unless Congress acts quickly, this corporation and others will be opening human-embryo farms."

The Advanced Cell Technology researchers say they cloned a six-cell human embryo starting with a donated female egg cell. They removed its nucleus and replaced it with a cumulus cell, complete with its genetic DNA. Cumulus cells normally help nurture eggs as they develop.

Such a technique could only yield replacement cells for women of childbearing age. But the researchers have also experimented with injecting cells with DNA from skin cells.

In a separate experiment, the researchers say they were able to develop a more advanced embryo, known as a blastocyst, in a process known as parthenogenesis. They bathed an egg cell with chemicals that changed its concentration of charged particles, reprogramming it to form an embryo.

The research was said to be very preliminary. Neither experiment was found to produce the master cells known as stem cells, which differentiate into other body tissues. Lanza and the company's top executive, Michael West, said they had no interest in transplanting such early embryos into a woman's womb to give birth to a cloned human being, nor was it clear that their embryo would be capable of that.

Researchers hope that they will eventually be able to develop and harvest stem cells from such embryos to grow replacement cells. They would be genetically compatible, because they would derive from a patient's own cells.

The company announced its findings Sunday online in The Journal of Regenerative Medicine. The research was also described online in Scientific American.

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

A critic of Advanced Cell Technology, who once sat on its ethics board, said the announcement was premature and would serve only to encourage opposition to cloning. The critic, Glenn McGee, a University of Pennsylvania bioethicist, called the announcement "nothing but hype."

He said the company's report lacks any significant details, including what cells company scientists actually grew from the cloned embryo.

"They are doing science by press release," he said.

The House of Representatives has voted to ban human cloning, and the Senate is considering such a ban.

"I believe it will be perhaps a big debate, but at the end of the day, I don't believe that we're going to let the cloning of human embryos go on," Sen. Richard Shelby, R-Ala., said on NBC's Meet the Press.

Bush is allowing federal funding of research on existing stem cell lines, but has been adamantly against anything more.

"The president has made it clear that he is opposed to any type of human cloning," White House spokeswoman Jennifer Millerwise said Sunday

Other research groups in this country and abroad also have plunged into cloning efforts. Some aim at reproductive cloning to produce a new person, but most hope to carry out therapeutic cloning to yield stem cells for treating spinal cord injuries, heart disease, cancer and other ailments.

A second company quickly claimed Sunday it had also cloned human embryos, but in unpublished research. That company, Clonaid, hopes eventually to clone human beings.

"I'm very pleased that I'm not alone," company director Brigitte Boisselier said. "We're doing embryos every day."

She refused to give details of the work. The company says it keeps its laboratory location secret for security reasons.

Many scientists say cloning of cows, sheep and other animals has produced some mysterious defects. They say the science is too weak to justify cloning a person, but they hold strong hope for cloning to produce replacement cells.

Dr. Norman Fost, director of the bioethics program at the University of Wisconsin-Madison, said the work of the Massachusetts researchers is "a basic part of making stem cell research useful for human beings." He said most Americans favor such science.

Carl Feldbaum, president of the Biotechnology Industry Organization, predicted that Congress will ultimately allow human cloning for therapeutic purposes.

"Therapeutic cloning has been gaining allies as its applications are understood," he said.

The Associated Press contributed to this report.