The Vatican has long held that human life begins at conception, but Benedict's comments were significant because he specified the position 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.
Benedict made the comments during an audience with members of the Pontifical Academy for Life, which opened an international 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 church's 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, however, did not specifically treat the question of the status of an embryo before it is implanted - 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 the mother's uterine cavity.
Benedict made clear, though, that there should be no moral distinction between an embryo before implantation and after.
"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 that 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.
"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 in their legislation regulating embryo research say life begins when an egg has been fertilized but the male and female chromosomes haven't yet mixed, 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, who was not a conference participant.
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 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 conference.
Pope John Paul II acknowledged in the encylical that a spiritual soul in an embryo cannot be determined scientifically, Eijk noted.
The conference will delve into the question of whether the embryo is a person, as well as the ethics of pre-implantation genetic diagnosis, on Tuesday.
