VATICAN CITY (AP) - The Vatican stressed Wednesday that it considers all research using stem cells from human embryos morally unacceptable, aiming to dispel any doubts about the stance Pope John Paul II laid out to President Bush.

In a meeting Monday, the pope urged Bush, who is weighing federal funding for work with stem cells, to reject research on human embryos.

Some observers and commentators later interpreted the pontiff's remarks as possibly exempting embryos created in fertility clinics and left over after a woman becomes pregnant.

In response, Vatican spokesman Joaquin Navarro-Valls issued a statement Wednesday saying the pope's condemnation applied to all research using stem cells from human embryos.

The statement quoted from a papal encyclical that said:

``This moral condemnation also regards procedures that exploit living human embryos and fetuses - sometimes `produced' for this purpose by in vitro fertilization - either to be used as `biological material' or as providers or organs or tissue for transplants in the treatment of certain diseases. The killing of innocent human creatures, even if carried out to help others, constitutes an absolutely unacceptable act.''

Embryonic stem cells are the basic building blocks for body tissue. To extract these cells for research requires killing the embryo - an action consistently rejected by the Roman Catholic church and other abortion opponents as the taking of human life.

In stem cell research, Bush faces one of the toughest issues of his young presidency.

Allowing federal funding could alienate some of America's 44 million Catholics, who make up an important political bloc. If Bush cuts or restricts the funding, he risks being accused of bowing to the pope and other religious and conservative leaders.

Bush said after meeting with the pontiff that he would take John Paul's views ``into consideration.''

The pope's statement, along with the clarification issued Wednesday, rule out one of the potential compromises the president is considering: research on stem cells derived from fertility clinic surpluses that would otherwise be discarded.

Scientists believe research using stem cells might unlock cures for diseases including Alzheimer's, Parkinson's and diabetes, as well as spinal cord injuries. The pope himself suffers from symptoms of Parkinson's disease.