The U.S. government broadened the definition of a human embryonic stem cell on Friday, helping qualify several corporate and academic experiments for federal funding.

Dr. Lana Skirboll, director of the Office of Science Policy of the National Institutes of Health, called the change technical and said it would be posted in the federal register for comment.

Human embryonic stem cells are the body's master cells, taken from very early stage embryos when they are just a ball of cells. The current definition describes them as cells taken from the inner layer of a blastocyst, a days-old hollow ball of cells. Skirboll said the new definition will include earlier stage embryos.

"We are making what I think is a relatively small technical change to the definition of human embryonic stem cells," Skirboll said in a telephone interview. "This changes none of the ethical requirements in the guidelines."

U.S. President Barack Obama lifted some restrictions on the federal funding of human embryonic stem cell research soon after he took office last year but the NIH imposed strict ethical requirements and a review process for funding.

Dr. Robert Lanza of Massachusetts-based Advanced Cell Technology, one of the companies seeking federal funding for its research, said the decision was important. His company is working with cells taken from embryos when they only have eight cells, with the aim of making it possible to implant the remaining seven-celled embryo into a woman to develop into a fetus.

"It would have been a disaster to exclude these valuable human embryonic stem cell lines from consideration for federal funding, especially since the leftover embryos used to generate them meet all the NIH requirements," Lanza said by e-mail. "In fact, it could be strongly argued that these human embryonic stem cell lines are more ethical since they can be derived without embryo destruction."

Opponents of human embryonic stem cell research believe it is wrong to destroy a human embryo for any reason and some oppose any research at all involving human embryos.