UNITED NATIONS - More than 100 countries on Monday launched the first UN talks aimed at achieving a legally binding ban on atomic weapons, as Washington led an international boycott of a process it deems unrealistic. Before the conference had even begun, the US ambassador to the UN, Nikki Haley, spoke out to reject the proposal in the light of current global security threats.

"As a mom and a daughter there is nothing I want more for my family than a world with no nuclear weapons," Haley, who represents the world's largest nuclear power, said on the sidelines of the meeting.

"But we have to be realistic," she added. "Is there anyone that believes that North Korea would agree to a ban on nuclear weapons?"

Haley spoke in a group of some 20 ambassadors from US allies who are boycotting the negotiations, including Britain, France and South Korea, Turkey and a number of countries from eastern Europe.

The ambassadors of Russia and China were notably absent, but both major nuclear powers are also sitting out the talks.

Haley estimated that "almost 40 countries" were not in the General Assembly on Monday. Some 123 UN members announced the nuclear weapon ban initiative in October, even as most of the world's declared and undeclared nuclear powers voted against. Leaders of the effort include Austria, Ireland, Mexico, Brazil, South Africa and Sweden, supported by hundreds of NGOs.

They say the threat of nuclear disaster is growing thanks to tensions fanned by North Korea's nuclear weapons program and an unpredictable new administration in Washington. But Britain, France, Israel, Russia and the United States all voted no, while China, India and Pakistan abstained. Even Japan - the only country to have suffered atomic attacks, in 1945 - voted against the talks, saying a lack of consensus over the negotiations could undermine progress on effective nuclear disarmament.

While acknowledging the promoters of the treaty were acting in "good faith," Haley said: "You have to ask yourselves: Do they really understand the threats that we have?"

Britain's ambassador to the UN, Matthew Rycroft asserted that his country "is completely committed to the long-term goal of a world without nuclear weapons" but said it does "not believe that those negotiations will lead to effective progress on global nuclear disarmament."

"The best way to achieve the goal of global nuclear disarmament is through gradual multilateral disarmament, negotiated using a step-by-step approach and within existing international frameworks," Rycroft added.

Haley noted that the United States had reduced its nuclear arsenal by 85 percent since the 1968 Treaty on the Non-Proliferation of Nuclear Weapons (NPT) took effect, and added "we are going to continue to do that."

But supporters of the UN process argue that little progress has been made in recent years despite commitments made by the major nuclear powers under the NPT.

And they point to successful grassroots movements that led to the prohibition of landmines in 1997 and cluster munitions in 2008 as a model for the future of nuclear disarmament.

"There was disappointment with the Obama administration, which made some pledges, but then ignored most of them," said Beatrice Fihn, director of the International Campaign to Abolish Nuclear Weapons, an international coalition of NGOs. "And now there are raised worries with the new US president."

Then-president Barack Obama announced a drive in 2009 to reduce the role of nuclear weapons and eventually eliminate them.

But his administration strongly encouraged NATO allies to vote against this year's UN negotiations, saying a ban would obstruct cooperation to respond to nuclear threats from adversaries.

President Donald Trump threatened a nuclear arms race in a tweet shortly before he took office in January, saying "we will outmatch them at every pass and outlast them all."

Nevertheless, with experience from the campaigns against cluster munitions and landmines, Fihn believes there is a "good chance" a treaty will be adopted, if not necessarily after the first phase of negotiations, which will end in July.

And such a treaty would oblige major powers to revisit their policies sooner or later - even if, like Russia and the United States, they're currently modernizing their nuclear weapons arsenal.

"Even if major (nuclear weapon) producers don't sign it, they have a big impact," Fihn said of global treaties. "Look at Russia denying using cluster bombs in Syria. Why? They did not sign (the cluster munitions ban), but they know it's bad."