The scientists at Oregon Health & Science University used skin cells from monkeys to create cloned embryos and then extracted embryonic stem cells from the embryos.
According to Shoukhrat Mitalipov and colleagues, this has only been achieved before in mice and the success of the research demonstrates that in principle at least, it is possible to clone humans and get stem cells from the embryos.
Some details of the research first surfaced at a conference in Australia in June, and another team of experts has since independently verified the work.
Mitalipov says though the efficiency is still low they are confident the technique will work in humans.
Scientists study embryonic stem cells because they are the source of every cell, tissue and organ in the body and it helps them understand the biology of disease and the prompts the development of new drugs and therapies.
The theory is that a small piece of skin taken from a patient can be used to grow tissue and possibly organs that are perfectly matched to the patient.
Embryonic stem cell research is a controversial issue and opponents believe it has sinister implications.
In the US, President Bush has repeatedly blocked legislation that would expand federal funding of such research.
Though many species of animals have been cloned, and experts have managed to extract stem cells from a variety of embryos, including human embryos, it has remained very difficult to both clone and then get embryonic stem cells from any animal.
This latest success by Mitalipov's team has transcended the two barriers of cloning a primate and then extracting embryonic stem cells from the clone.
Primates are the group of mammals that includes monkeys, apes and of course humans.
Cloning involves removing the genetic material from an egg and replacing it with the DNA from an adult cell.
The technique, somatic cell nuclear transfer, involves taking the nucleus from an adult cell, in this case fibroblasts, (a type of skin cell) from nine adult males.
An egg cell is then hollowed out and the nucleus from the adult cell inserted; this in turn programs the egg into behaving as if it had been fertilized and encourages it to grow into an embryo.
This is not an easy process and the modified technique cuts the amount of damage done to the eggs but despite the adoption of the modified technique, 304 eggs from 14 rhesus macaque monkeys were used before two stem cell lines were produced.
Apparently, the dyes used in cloning some animals are toxic to primate cells.
The researchers say much work will be needed before the process could be applied to human eggs.
Mitalipov says the embryonic stem cells were found to be truly pluripotent - able to develop into any kind of cell found in the body - and they were able to develop them into heart cells and nerve cells.
Mitalipov says to date the team has failed to produce cloned monkeys that could grow into live baby monkeys by using the somatic cell nuclear transfer technique.
He says his team will not try to clone humans but they hope the techniques they have developed will be useful for other scientists working with human eggs.
Experts say the research makes the creation of cloned human embryos a realistic possibility and say the stem cells they could provide would be invaluable in the search for new treatments for incurable conditions such Alzheimer's, Parkinson's and motor neurone disease.
They say the breakthrough has huge implications in terms of new therapies but many critics who are wary of such research say the breakthrough heralds a potential 'ethical nightmare'.
The research is published in the journal Nature.
