The embryos contain stem cells which can be used to create almost any human tissue. Diseases such as diabetes and muscular dystrophy damage this tissue.

The scientists hope that cloned embryos will one day be used to replace tissue damaged by disease.

But they say they will never try to produce cloned human beings.

For a human being to be created, a cloned embryo would have to be implanted into a woman who would then have to give birth.

Some people say all forms of human cloning, even for medical research, should be banned.

Early stages

The US and South Korean scientists say their human embryo clones are the "most advanced yet produced".

However, the idea of using cloned embryos for tissue transplants is still in its early stages.