The US had thrown its weight behind an alliance of countries, led by Costa Rica, pushing for a global ban on cloning human embryos.

But UN members have dropped plans for a treaty because of deadlock over the merits of cloning for medical research.

Pro-cloning campaigners have greeted the decision as a victory.

"This is a very good result," said Bernard Siegel, director of the Genetics Policy Institute, which lobbies for the use of cloned human embryos in medical research.

Stalemate

UN diplomats abandoned a planned vote on two competing motions on Thursday when it became clear that neither camp had enough support.

One resolution, drawn up by Costa Rica and backed by the US and 60 other countries, called for a treaty to ban all cloning as unethical and morally reproachable.

A second motion came from Belgium. It was designed to keep the door open for medical research on stem cells taken from cloned human embryos, known as therapeutic cloning.

Many scientists believe therapeutic cloning offers hope of cures for a range of diseases, such as Alzheimer's.

Belgium's resolution would have allowed individual countries the choice on whether to ban therapeutic cloning, while backing a treaty banning cloning for reproductive purposes, something which all 191 UN members oppose.

Instead of a treaty, UN members agreed on Thursday to discuss the wording of a declaration - a much weaker device - on cloning in three months' time.

"There is such division in the international community that any treaty would not make it, so the idea of the declaration is to find some general language that we could all live with," said Belgian diplomat Marc Pecsteen.

An official at the US State Department presented the shelving of the treaty plan as "a moderate success", saying it had "prevented any action by the UN that would endorse human cloning".

Compromise

UN members faced a deadline of 19 November to agree on the scope of any possible treaty, or miss the final meeting this year of the UN General Assembly's legal committee, which drafts treaties.

Faced with a stalemate, it adopted Italy's suggestion of replacing the treaty plan with talks on a declaration.

Human embryo cloning is controversial in many countries.

In the US, it became an election issue in the 2004 presidential poll. President George W Bush has frequently spelt out his support for a total ban, drawing criticism from former first lady Nancy Reagan, whose late husband Ronald suffered from Alzheimers disease.

In the UK, regulators this year gave the go-ahead for UK-based scientists to carry out therapeutic cloning.