Scientists have reacted with anger to US President George W Bush's decision to veto a bill allowing federal funding for new embryonic stem cell research.
They argue it will damage a promising field of medical research.
Leading researchers labelled Mr Bush "hypocritical", "out of touch" and "selfish" over his decision not to sign into law a bill approved by Congress.
Mr Bush argued that the law "crossed a moral boundary that our decent society needs to respect".
Polls suggest most Americans back the research, which scientists hope will lead to cures for serious illnesses such as Alzheimer's, Parkinson's and diabetes.
The vetoed bill, the Stem Cell Research Enhancement Act, would have scrapped limits on federal funding imposed by Mr Bush in 2001. It was the first time in his presidency that Mr Bush refused to sign into law a bill approved by Congress.
The bill failed to reach the two-thirds majority in its Senate vote which would have overturned the presidential veto.
In Britain, the President's decision drew anger and derision from the research community.
It re-emphasised "how out of touch he is with rational thinking on this issue," said Robin Lovell-Badge, head of developmental genetics at the National Institute for Medical Research.
The blocking of federal funds for research on embryonic stem cells is "slowing down the global effort to develop therapies for a range of diseases and illnesses," added Martin Rees, president of the Royal Society.
Mr Bush summed up his opposition to the bill on ethical grounds. "This bill would support the taking of innocent human life of the hope of finding medical benefits for others," he said.
But Graeme Laurie, an expert in the legal side of medicine from Edinburgh University, said there was an "underlying hypocrisy" in Mr Bush's position.
"The stated reason for President Bush's objection to embryonic stem cell research is that 'murder is wrong'; why then does he not intervene to regulate or ban [embryonic] stem cell research carried out with private funds and which is happening across the US?" he asked.
"It is a strange morality indeed that pins the moral status and life of the embryo on the question of who is paying for the research."
No new lines
The 2001 federal funding regulation provides government money only for lines of stem cells that already existed when the order came into effect, not for any new lines.
Opinion polls suggest most Americans back the research
But US researchers say that sticking to these lines restricts progress.
Jeffrey Balser, associate vice-chancellor for research at Vanderbilt University in Nashville, said US institutions were "on the threshold of phenomenal progress in stem cell research.
"But we are being slowed by these federal restrictions," he told The Tennessean website and newspaper.
The Senate vote came at the end of two days of emotional debates, which included consideration of two other related bills.
One was signed into law by President Bush. It bans the growing and aborting of foetuses for research.
The other sought to encourage stem cell research using cells from sources other than embryos. Although passed by the Senate, it fell in the House. Mr Bush said he was disappointed this bill failed to get through.
"It makes no sense to say that you're in favour of finding cures for terrible diseases as quickly as possible and then block a bill that would authorize funding for promising and ethical stem cell research," he said.