Pope Benedict XVI said Monday that embryos developed for in vitro fertilization deserve the same right to life as fetuses, children and adults — and that that right extends to embryos even before they are transferred into a woman's womb.

The Vatican has long held that human life begins at conception, but Benedict's comments were significant because he specified that even an embryo in its earliest stages — when it is just a few cells — is just as much a human life as an older being.

The pope made the comments during an audience with members of the Pontifical Academy for Life, who opened a Vatican-sponsored conference Monday on the ethics surrounding the handling of embryos before they are implanted during in vitro procedures.

The Vatican opposes in vitro procedures because embryos created in a laboratory are often discarded, whereas others are frozen and still others are created solely for experimentation or to create stem cells.

Benedict repeated the Roman Catholic Church position that life begins at the moment of conception and deserves to be respected and protected from that moment on — a position set out most authoritatively in the 1995 encyclical "Evangelium Vitae."

That encyclical did not specifically address the status of an embryo before it is implanted after in vitro fertilization — the two or three days of growth in a laboratory during which the fertilized egg is dividing into a group of cells that are transferred by a doctor into a woman's uterus.

Benedict made clear that there should be no moral distinction between an embryo before implantation and after — even though he acknowledged there is no explicit teaching on the first days of life in Scripture.

"The Magisterium of the church has constantly proclaimed the sacred and inviolable character of every human life, from its conception to its natural end," he said.

"This moral judgment is valid already at the beginnings of life of an embryo, before it is implanted in the womb of the mother, who will care for it and nourish it for nine months until the moment of birth," he said.

"The love of God doesn't make any difference between the newly conceived, still in the womb of his mother, and the baby, or the young person, or the mature man or the old man," he said. "He doesn't make the distinction because in each of them he sees his own image and similarity."

While there is no consensus among scientists about when life begins — and thus deserves legal protection — many scientists believe life starts when the first neurological tissues are evident, about two to three weeks after fertilization, said Dr. Jacques Cohen, a reproductive scientist in New York who was not at the conference.

"Scientists draw lines at different points," said Cohen, who runs the largest pre-implantation genetic diagnosis group in the United States, Reprogenetics, as well as the Galileo Research Laboratories, which researches embryonic development.

Some countries have legislation regulating embryo research that says life begins when an egg has been fertilized, he said. Some philosophers argue life begins with consciousness — much later on.

"I think we should not draw lines. I think we should treat all stages with a great deal of respect," particularly considering how difficult it is to obtain eggs for in vitro procedures, said Cohen.

Catholic church teaching holds that in vitro fertilization is morally wrong because it replaces the "natural" conjugal union between husband and wife, and often results in the destruction of embryos. The Roman Catholic Church also condemns all forms of experimentation on human embryos.

"Evangelium Vitae" spelled out the Vatican's position, but it sidestepped the issue of when precisely conception occurs, Monsignor Jacobus Eijk, a moral theologian and bishop of Groningen, the Netherlands, said in a paper to be delivered at the Vatican conference.

Pope John Paul II acknowledged in the encylical that a spiritual soul in an embryo cannot be determined scientifically, Eijk noted. But in the encyclical, John Paul said research on the embryo provided a "valuable indication for discerning by the use of reason a personal presence at the moment of the first appearance of human life: How could a human individual not be a human person?"

On Tuesday, the conference will delve into the question of whether the embryo is a person, as well as the ethics of pre-implantation genetic diagnosis.