Scientists have received the news that a human embryo has been cloned into a woman with a large dose of scepticism and are challenging the maverick fertility expert to prove it.
US-based Dr Panos Zavos said today some secrecy had to be maintained in his work and he stood by his announcement that he had transplanted the embryo into a 35-year-old-woman less than two weeks ago.
The claim bore a striking resemblance to an announcement made last year by the Raelian Movement - a cult that believes life on Earth was engineered by visitors from outer space - saying it had produced the world's first cloned human.
It never came up with any scientific evidence but managed to whip up huge publicity around the world.
Scientists are now throwing down a similar gauntlet to Dr Zavos, urging him to publish his results so they can be reviewed by experts.
"Like most scientists and doctors I remain extremely sceptical of the claims," said Dr Bob Ward from the Royal Society, Britain's main academy of science.
Dr Zavos told BBC radio he had worked in the reproductive arena for 25 years or more and had "delivered everything that he said that he would".
"We have to maintain some secrecy in our work," Dr Zavos said. Why? Because a lot of people would like to know where we are, what we do and reveal everything."
Sceptics point to similar claims, like the Raelian Movement, that have fizzled out as no evidence has been forthcoming.
Italian fertility doctor Severino Antinori, a former colleague of Dr Zavos, said nearly two years ago that three women were pregnant with clones. He too produced no evidence but became a household name in Italy following his claims.
Dr Peter Braude, a fertility expert at King's College London said: "Zavos does not represent mainstream science and what and his colleagues are doing is seeking publicity rather than advancing science."
"It is highly unlikely that he has successfully made a cloned human embryo," Professor Chris Higgins of Britain's Medical Research Council said of Dr Zavos. "So far he has produced no data at all."
Even Dr Zavos admitted the chances of the woman's pregnancy going to term were slim. He said he would continue until he was successful and was looking for more volunteers.