One project member has predicted that a baby will be born within two years using the technique. But, apart from strong ethical concerns, critics say that the technique's low expected success rate makes it unsuitable for human cloning.

Although many researchers and politicians have chosen to ignore the latest claims being made for the project, reports that a Japanese researcher is involved led to the prime minister's intervention.

A law passed last December, which comes into effect this June, outlaws human cloning in Japan. Mori said he was charging the Ministry of Education, Culture, Sports, Science and Technology, and Takashi Sasagawa, the science minister, to take steps to keep Japanese researchers out of the project.

"We will try to persuade researchers that what they are doing is wrong and explain that it is a violation of Japanese law," says an official in Sasagawa's office. But participating in such a research project abroad would not directly violate Japanese law — although researchers might be reluctant to defy the government's wishes, and research agencies may cut their funding if they do.