Scientists in the United States say they have created the world's first cloned embryo from a monkey, in work that could spur cloning of human cells for use in medical research.

In a paper published online by the British journal Nature, a team in Oregon said they had created cloned embryos of rhesus macaques, using the same method that famously led to Dolly the Sheep and other genetically duplicated animals.

It is the first time that this technique has been successfully used to create cloned primate embryos.

The group generated two lines of embryonic stemcells from the embryos, according to the research headed by Shoukhrat Mitalipov of the Oregon Health and Science University in Beaverton, Oregon.

Dolly, the world's first cloned animal, was created in 1996, by using so-called somatic cell nuclear transfer (SCNT) in which the genetic core of an egg is removed and replaced with the nucleus of an adult cell.

The egg is then stimulated with chemicals or a jolt of electricity to prompt its division.

The list of other cloned creatures using SCNT includes mice, pigs, cats, cows and dogs.

Until now, though, there has been no cloned primate, for researchers have encountered obstacles that cause cell development to be catastrophically flawed.

Work on primate cloning has also stirred controversy among ethicists, who say it could open the door to cloning human beings, not just cells. In an exceptional move, Nature said it moved forward the release of the paper because of continuing speculation.

Researchers distinguish between reproductive cloning of humans, in which a putative cloned baby would be born and therapeutic cloning, in which only cloned cells would be used for medical reasons and no baby would result.