London: Scientists claim to have for the first time created viable artificial sperm using stem cells, a major breakthrough which they say could lead to new treatments for infertile men.

A team at Kyoto University in Japan has created the sperm-producing germ cells in a laboratory and transferred them into infertile mice, which after the treatment were able to produce healthy offspring, a newspaper reported.

The development could help thousands of infertile men become fathers if the method proves similarly effective in humans, say the scientists.

In fact, they used stem cells from mouse embryos to create primordial germ cells, which drive the production of sperm in men.

When transplanted into testicles of infertile mice, the cells produced normal-looking sperm.

The team, led by Dr Katsuhiko Hayashi, injected the sperm into mouse eggs and implanted them into female mice, which give birth to healthy pups. The babies, when they grew up, were capable of reproducing naturally.

Previous experiments to make sperm from embryonic stem cells have not been so successful, and in most cases led to unhealthy offspring which soon died.

Experts have hailed the latest findings published in the Cell' journal.

Fertility expert Dr Allan Pacey of the University of Sheffield said: "This is quite a step forward in developing a process by which sperm could be made for infertile men perhaps by taking as a starting point a cell from their skin or from something like bone marrow."

Dr Jane Stewart, British Fertility Society spokesperson, said the ability to create human sperm-producing cells in the lab would be a "landmark achievement" in fertility treatments.

She added: "This publication in an animal model marks a further step towards this goal, however as the authors clearly point out much work remains to be done."