A human cloning breakthrough last night raised hopes for tackling crippling diseases - and fears that the birth of the first cloned baby was now inevitable. A private research firm in America announced it had made the "milestone" breakthrough of creating human embryos from cloned human cells.

Scientists said they had produced "preimplantation embryos" but were aiming to use them for research to treat disease, not to create a cloned human being.

But some experts said the research could be abused to produce the first human clone, and called for international laws to ban the practice.

Human embryo clones have become a "holy grail" in the scientific community because the embryos contain stem cells, which can be used to create virtually any human tissue. They are potentially vital for transplant operations and for therapies for conditions such as strokes, cancer, Aids, Alzheimer's disease and Parkinson's. But scientists also fear that maverick doctors could use the technology to try to create clone babies, creating an ethical minefield over possible health risks and human rights issues.

The breakthrough came only one day before new laws on embryo research designed to close a legal loophole in Britain were due to be debated, in the House of Lords today, and in the Commons on Thursday.

The emergency legislation - prepared after the High Court ruled that cloned embryos were not covered by earlier laws and that, in effect, cloning humans was no longer illegal -would ban cloned embryos from being implanted into wombs.

The legislation does not ban therapeutic cloning using cell nuclear replacement - the technique used by the American firm and to produce Dolly the sheep - for research.

The American firm, Advanced Cell Technology (ACT), based in Worcester, Massachusetts, announced its breakthrough in an online journal, e-biomed, which said it was "the first proof that reprogrammed human cells can supply tissue for transplantation".

The firm said it had cloned embryos by removing the DNA from human egg cells.

The DNA from an adult human body cell was then implanted into the egg cell, which was then stimulated to grow into a six-cell embryo.

One of the ACT team, Dr Michael West, said the firm had no plans to clone a human being.

"We could implant these cells into a woman's uterus and make a cloned human being, but that's not what we are doing,"he said.

"We are doing it to help cure diseases. We are making cellular life, not a human life." Dr West said it would be a few years until his technology could be applied to curing diseases, adding: "These are the first faltering steps towards this new area of medicine."

Dr Ian Wilmut, who led the team which produced the Dolly the sheep clone at the Roslin Institute, Edinburgh, said the report was a "very preliminary observation". But Dr Patrick Dixon, an authority on the ethics of human cloning, warned the breakthrough could open the door to producing full-scale human clones.

"It is now only a matter of time before a clone human is born," he said. "There are huge potential risks in that process, including grotesque mutations and hidden disabilities."