The biggest scientific furore so far about human cloning has broken out in Washington, with a clash between a small group of researchers who are determined to create cloned babies and a larger number who say the procedure is extremely risky.
Severino Antinori, an Italian fertility specialist, and Panayiotis Zavos, a US colleague, told a meeting organised by the National Academy of Sciences that they could screen out abnormal embryos. They plan to start the process later this year in an unspecified country where human cloning is legal.
Brigitte Boisselier, a biochemist associated with the Raelian cult, is working on a separate human cloning project.
Mainstream scientists denounced both projects. Leading the attack was Rudolf Jaenisch, an animal cloning pioneer at the Massachusetts Institute of Technology, who said: "At present there is no way to predict whether a given clone will develop into a normal or abnormal individual."
The procedure that produced Dolly the sheep, the first cloned mammal, in Scotland in 1997 has also succeeded with cattle, pigs, mice and other species - but at a huge cost in abnormal embryos that were spontaneously aborted or died soon after birth.
Dr Zavos and Dr Antinori said 1,500 couples, mainly in the US and Italy, had volunteered to take part in their cloning project because infertility would otherwise prevent them having children. The doctors would choose 200 of them for the first stage of the project.
The Food and Drug Administration has prohibited human cloning in the US, in the absence of federal legislation to ban it. Legislation to ban human cloning has been passed in several countries including the UK and Italy. In the US a proposed legislative ban on reproductive cloning has been caught up in a controversy about therapeutic cloning - cloning embryos as a source of stem cells for research rather than to produce babies.