Researchers removed DNA from donated human eggs, and replaced it with DNA from the skin cells of two volunteers.

They produced embryos with genetic material that matched the men’s, but did not go on to extract stem cells.

UK experts say the research, published in the journal Stem Cells, is a small but not a great step forward.

The team at Stemagen Corporation in La Jolla, California, says the work could be an important stage in developing embryonic stem cells for patients.

The group produced five embryos called blastocysts from 25 donated eggs. DNA fingerprinting proved that at least one of these was a clone.

“We’re the first in the world to take adult human cells and then document that in fact we were able to clone embryos from them,” lead researcher Dr Samuel Wood told the BBC.

He said the embryos were destroyed in the process of verifying they were clones, but they were now working on creating stem cell lines.

Dr Lyle Armstrong of Newcastle University is one of a handful of other researchers who have made cloned human embryos using a technique known as nuclear transfer pioneered in Dolly the sheep. Unlike the US team, the Newcastle group used DNA from embryonic rather than mature tissue.

Dr Armstrong said the US study showed that the objective of using cells from an adult person to make individual stem cells might one day be possible.

“It’s a small step but not a great step forward,” he told BBC News. “It’s interesting that they’ve been able to repeat somatic cell nuclear transfer and get embryos of the stage where embryonic stem cells could be derived, but it is disappointing that they’ve failed to derive a stem cell line.”

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