An Italian fertility expert says a patient will give birth to a cloned baby early next year but experts, including one who helped create Dolly the sheep, are sceptical.
Dr Severino Antinori told a news conference in Rome on Tuesday that the cloned baby is due in January.
The maverick doctor gained fame nearly a decade ago when he helped a 62-year-old woman give birth following fertility treatment with a donated egg, but he has revealed few details about his latest project.
"It's going well. There are no problems," was all he would say about the pregnancy of the cloned embryo.
He gave no clues about the woman's identity, age, where and when the embryo was cloned and where she would give birth, nor of two other women he said are carrying cloned embryos.
All he would say was that the cloned foetus was healthy and weighed roughly 2.7 kilogrammes.
Other experts in the field have grave doubts. "It is possible but I am highly sceptical. It is unlikely to be true," Professor Anne McLaren, of the Wellcome Trust Cancer Research UK Institute at the University of Cambridge, told Reuters yesterday.
Cloning experts doubt Antinori or his unknown colleagues have the expertise to clone a human. Although sheep, mice and pigs have been cloned, scientists have not yet produced a carbon copy of any primate.
Experts at the Roslin Institute in Scotland, where Dolly was created, said that without proof it is impossible to know what Antinori has done.
"It is very difficult to know if there is any substance behind these claims at all," Dr Harry Griffin said when Antinori said a woman in his programme was pregnant in April.
Antinori did not produce any evidence then or now so scientists do not know if he has achieved anything or if he is just seeking publicity.
"We have nothing more to add," a spokesman for the institute said yesterday.
Dolly the sheep was cloned using a technique called nuclear transfer. The nucleus of an egg cell was removed and replaced with the nucleus from a cell of the animal to be cloned. It was then reprogrammed so the cell grew and divided normally.
It is a skilled and risky technique. Only a small percentage of clones result in pregnancies and there is a high percentage of miscarriages and deformities.
Even animal clones that look healthy may have genetic abnormalities or be predisposed to a decreased life span because the cells used in the cloning process acquire DNA damage as they age.
Dolly is thought to be older than her years because she was produced from a cell taken from a six-year-old ewe.
Antinori has not given any clues about how the human embryo was cloned nor who the progenitor, the person who has been cloned, is.
"We will wait and we will see what the DNA studies show if a baby is born," McLaren said. "I just hope it will not have abnormalities."
Comparing DNA from the progenitor and from the baby will determine whether the baby is genetically identical and a clone.
"I would not rule out the possibility that he has managed to do this but I would fear for what the consequences might in terms of deformities," said Dr Sandy Thomas.
Thomas, director of the Nuffield Council on Bioethics which examines ethical issues arising from developments in medicine and biology, said Antinori is not following the normal criteria by which scientific advances are judged.
"No one can therefore make any kind of an evaluation of the validity of what he is saying. There is no information so it is impossible to make a judgment," she added.