A US court on Monday ordered a temporary halt to federal funding of embryonic stem cell research, which President Barack Obama had authorized, saying it involved the destruction of human embryos.
US District Court Judge Royce Lamberth ruled in favor of a coalition of groups, including several Christian organizations, which had sought a temporary injunction on funding of the research ahead of a planned lawsuit.
"Plaintiffs have demonstrated a strong likelihood of success on the merits," Lamberth said.
"ESC (embryonic stem cell) research is clearly research in which an embryo is destroyed," Lamberth's ruling said.
"To conduct ESC research, ESCs must be derived from an embryo. The process of deriving ESCs from an embryo results in the destruction of the embryo. Thus ESC research necessarily depends upon the destruction of a human embryo."
Obama's decision to reverse the ban on federal funds for ESC research was lauded by many researchers who believe the field has huge potential for treating serious diseases including Alzheimer's, Parkinson's and diabetes.
Researchers believe that stem cells, so-called because they are the foundation for all human cells, provide two promising avenues for scientists.
First, they can be used for research that cannot be performed inside the body. But scientists believe they can also coax the foundational cells into cardiac, pancreatic or brain cells to replace damaged or infected cells and allow tissue or organs to reconstitute themselves.
In reversing the ban put in place by his predecessor George W. Bush, Obama pointed to the potential breakthroughs the research could yield, and he rejected the "false choice" between sound science and moral values.
But the research is fiercely opposed by religious conservatives, who believe that life begins at conception, because it involves the disposal of embryos.
In 1996, Congress enacted legislation known as the Dickey-Wicker amendment that bans federal funding for research in which human embryos are either destroyed or discarded.
But the Obama administration argues that the research itself does not require disposal or destruction of the embryos, which were created for in-vitro fertilization treatments but never used.
Lamberth rejected that distinction.
"Simply because ESC research involves multiple steps does not mean that each step is a separate 'piece of research' that may be federally funded," he wrote. "If one step or 'piece of research' of an ESC research project results in the destruction of an embryo, the entire project is precluded from receiving federal funding by the Dickey-Wicker Amendment."
He also dismissed claims that researchers would be unfairly targeted by a halt, saying they could still seek private funding.
And he said that because there was no conclusive proof that ESC research could help Parkinson's or Alzheimer's sufferers, the suggestion that they would be harmed by the injunction was "speculative."
The Justice Department said it was "reviewing the judge's decision."
The administration could choose to appeal the temporary injunction, or wait until the lawsuit is argued in court.