British scientists say they have cloned the country's first human embryo.
The Newcastle University team took eggs from 11 women, removed the genetic material and replaced it with DNA from embryonic stem cells.
The aim of this kind of work - the subject of fierce debate - is to make cloned embryos from which stem cells can be used to treat diseases.
Meanwhile South Korean scientists say they have created stem cells to match individuals for the first time.
Stem cell lines were created by taking genetic material from the patient and putting it into a donated egg.
The resultant cells were a perfect match for the individual and could mean treatments for diseases like diabetes without problems of rejection.
Therapeutic cloning - believed to have huge potential to treat disease and disability - is allowed in Britain.
Reproductive cloning - the cloning of human embryos with the intention of creating a baby - was made illegal in 2001.
"We are talking about several years before we are talking about a cell-based therapy that can go back into the patient"
The use of embryonic stem cells is controversial, with opponents arguing that all embryos, whether created in the lab or not, have the potential to go on to become a fully fledged human. Others fear there are safety concerns.
Supporters of cloning say it could offer numerous benefits in the future, such as fighting disease, battling infertility or preserving endangered species.
'Unsafe and inefficient'
Criticising the Newcastle research, Julia Millington from the ProLife Alliance said cloning for research purposes was profoundly unethical.
Josephine Quintavalle from CORE said: "No matter how it is created, a human embryo's destiny should be to live and not to be turned into human stem cells."
Life said cloning was "unsafe and inefficient", and involved exposing women to dangerous fertility drugs in order to collect sufficient eggs.
STEM CELLS
The critical factor for success appeared to be how quickly the egg was collected and manipulated, Professor Alison Murdoch and colleagues found.
The clone that lasted for five days had been collected and manipulated within 15 minutes.
Other tissues
Stem cells have the ability to develop into virtually any tissue in the body and could, in theory, be used to replace damaged cells in conditions such as Parkinson's disease and diabetes.
HAVE YOUR SAY
"We are talking about several years before we are talking about a cell-based therapy that can go back into the patient," she said.
Colleague Dr Miodrag Stojkovic said: "I'm really happy but I know that this is just the beginning of a long journey so we have to continue to try to derive stem cells that will definitely help us one day to cure diseases."
The UK research is published in Reproductive and BioMedicine Online.
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