Leading scientists are concerned that reports of a woman being pregnant with a cloned baby could lead to a halt in stem cell research in the United States.

They fear that controversy over reports of what would be the world's first cloned human could tip the US Senate in favour of banning the cloning of embryos for stem cell research. Such a ban would seriously undermine work that offers the possibility of cures for many diseases.

“My worry is that it is going to do very severe damage to the legitimate application of cloning,” said Dr Robert Lanza, head of …