A cloning scientist yesterday rejected accusations that his work was exploitative, unsafe and socially unacceptable.

Panayiotis Zavos, of the Centre for Reproductive Medicine in Lexington, Kentucky, claims he can produce hybrid embryos by injecting cow eggs with DNA from dead humans.

His experiments used DNA "donated" after bereaved relatives contacted him, said Dr Zavos. Such experiments would be illegal in Britain.

One set of embryos, from a man aged 33 thought to have died in a car crash, divided into 64 cells, theoretically mature enough to implant. Dr Zavos said there was never any intention to try to create a cloned human - the embryos would have been rejected because they were created from cow eggs. But, he said, his experiments paved the way to create cloned babies with cells taken from the dead. "This is a very important development in our work," he said.

To the dismay of other scientists, Dr Zavos has openly declared his hope to clone a human. Earlier this year, he announced that a woman implanted with a cloned embryo at his clinic had failed to become pregnant.

"It is grossly misleading to suggest you can replicate a loved one, such as a child lost in a road accident, by producing a cloned person with the same genetic material," said Richard Gardner, a professor who chairs the Royal Society working group on stem cell research and cloning. "Even more worrying is that Dr Zavos sees this work as a first step towards human reproductive cloning.

"Evidence shows reproductive cloning is medically unsafe, scientifically unsound, and socially unacceptable."