WASHINGTON (AP) -- President Barack Obama says "medical miracles do not happen simply by accident."
That's why he says he's allowing federal taxpayer dollars to fund broader research on embryonic stem cells.
Obama has signed an executive order reversing a 2001 directive by his predecessor.
President George W. Bush limited the use of taxpayer money to the 21 stem cell lines that had been produced before his decision, out of concern about the destruction of human embryos.
Obama's order is aimed at increasing research into possible cures for ailments from diabetes to paralysis.
He called his decision a "difficult and delicate balance."
The president insisted that his order would not open the door to human cloning, which he called "profoundly wrong." He said strict guidelines will be developed and enforced to ensure that.
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