US lawmakers approved plans to expand government funding for stem-cell research using human embryos, defying a promised veto by President George W Bush, who called the measure a "grave mistake."
The Democratic-led lower House of Representatives on Thursday, passed the measure by 247-176 votes, more than 40 votes short of the two-thirds margin needed to override a presidential veto. Bush in July 2006 rejected a virtually identical bill passed by a Republican-led Congress.
The plan sets up a clash between ethics and scientific progress and forces US taxpayers "to support the deliberate destruction of human embryos," Bush said in a statement on Thursday.
"Crossing that line would be a grave mistake," he said, adding that he would veto the bill.
Scientists believe stem-cell research holds the promise of cures for diseases such as Alzheimer's, Parkinson's and diabetes, but the debate over the use of embryos has caused years of emotional debate that has cut across party lines.
Opponents of research that uses embryos discarded after in-vitro fertilization argue that other sources are equally promising and less morally controversial, including adult stem cells from nasal tissue, umbilical cord blood, bone marrow and fatty tissue.
"Destroying nascent human life for research raises serious ethical problems, and millions of Americans consider the practice immoral," the White House said in a separate statement.
Under a policy adopted by Bush in 2001, federal funding for embryonic stem-cell research is limited to about 20 lines of human embryonic stem cells that existed at the time.
"Researchers have been investigating innovative techniques that could allow doctors and scientists to produce stem cells just as versatile as those derived from human embryos, but without harming life," Bush said on Thursday in a statement issued from the Group of Eight (G8) summit in Germany.
US newspapers reported on Thursday that scientists turned mouse skin cells into what are in effect embryonic stem cells, signalling a potential breakthrough in the debate if the process works in humans.
Bush, a born-again Christian, has refused to open up federally funded research to more stem-cell lines for a mix of moral, religious and political reasons.
Democratic Congresswoman and House speaker Nancy Pelosi, a Roman Catholic, evoked religion in remarks on the chamber's floor urging Bush to approve the bill.
"Science is a gift of God to all of us and science has taken us to a place that is biblical in its power to cure and that is the embryonic stem cell research," she said.
The House originally approved the bill in January. After the Senate passed its own version in April, a second House vote was needed.