US scientists involved with a small company set up by an unnamed investor report they are the first to clone human embryos and prove it.

But some researchers are asking how much of a scientific development this really is.

Dr Andrew French of Stemagen Corporation of La Jolla in California and colleagues have published their findings online ahead of print publication in the journal Stem Cells.

The researchers used somatic cell nuclear transfer (SCNT) to clone five early-stage embryos, called blastocysts, from donated human eggs and skin cells from two men.

"This study demonstrates, for the first time, that SCNT can produce human blastocyst stage embryos using nuclei from a differentiated adult somatic cell," the researchers say.

Instead, they destroyed the embryos in the process of checking their DNA in order to prove they were clones.