Haley told reporters the countries skipping the negotiations are instead committed to the Non-Proliferation Treaty, which entered into force in 1970 and is aimed at preventing the spread of nuclear weapons and weapons technology.
"There is nothing I want more for my family than a world with no nuclear weapons. But we have to be realistic. Is there anyone that believes that North Korea would agree to a ban on nuclear weapons?" Haley told reporters.
The United Nations General Assembly adopted a resolution in December -- 113 in favour to 35 against, with 13 abstentions -- that decided to "negotiate a legally binding instrument to prohibit nuclear weapons, leading towards their total elimination" and encouraged all member states to participate. "You are going to see almost 40 countries that are not in the General Assembly today," Haley said. "In this day and time we can't honestly that say we can protect our people by allowing the bad actors to have them and those of us that are good, trying to keep peace and safety, not to have them."
The Trump administration is reviewing whether it will reaffirm the goal of a world without nuclear weapons, a White House aide said last week, referring to an aim embraced by previous Republican and Democratic presidents and required by a key arms control treaty.
Britain's UN Ambassador Matthew Rycroft said: "The UK is not attending the negotiations on a treaty to prohibit nuclear weapons because we do not believe that those negotiations will lead to effective progress on global nuclear disarmament." Deputy French UN, Ambassador Alexis Lamek said the security conditions were not right for a nuclear weapons ban treaty.
"In the current perilous context, considering in particular the proliferation of weapons of mass destruction and their means of delivery, our countries continue to rely on nuclear deterrence for security and stability," Lamek said.
Beatrice Fihn, executive director of the International Campaign to Abolish Nuclear Weapons, said in a statement: "It is disappointing to see some countries with strong humanitarian records standing with a government which threatens a new arms race."
More than 100 countries are set to launch the first UN talks on a global nuclear weapons ban over objections from the major nuclear powers.
Some 123 UN members announced in October that they would launch the UN conference to negotiate a legally binding nuclear ban treaty, even as most of the world's declared and undeclared nuclear powers voted against the talks.
Britain, France, Israel, Russia and the United States 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 the lack of consensus over the negotiations could undermine progress on effective nuclear disarmament.
The countries leading the effort include Austria, Ireland, Mexico, Brazil, South Africa and Sweden. Hundreds of NGOs back their efforts.
They say the threat of nuclear disaster is growing thanks to mounting tensions fanned by North Korea's nuclear weapons programme and an unpredictable new administration in Washington.Supporters point to successful grassroots movements that led to the prohibition of landmines in 1997 and cluster munitions in 2008.
"I expect that this will take a long time, let's not be naive," Swedish Foreign Minister Margot Wallstrom said at the UN last week."But it's very important in these days when you see more of this rhetoric, and also sort of power demonstrations, including threatening to use nuclear weapons."
"Quite a high number of countries are actually interested in saying we have to break the deadlock that has been on this issue for so many years," she added. "So it's also the expression of frustration."
No progress has been made on nuclear disarmament in recent years despite commitments made by the major nuclear powers to work toward disarmament under the 1968 Non-Proliferation Treaty (NPT), said Beatrice Fihn, director of the International Campaign to Abolish Nuclear Weapons, an international coalition of NGOs.
"There was disappointment with the Obama administration, which made some pledges, but then ignored most of them," she said. "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." However, with experience from the campaigns against cluster munitions and landmines, Fihn believes there's a "good chance" a treaty will be adopted, if not necessarily after the first phase of negotiations, which will end in July.
Even with the major nuclear powers boycotting the debate, a treaty would oblige them to revisit their policies sooner or later -- even if, like Russia and the United States, they're currently modernising 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 munition ban), but they know it's bad."
Fihn compares such arguments to the logic of chain smokers: "It's never the right time to quit." "But with the multipolar world, lots of countries feel like they don't have to wait for the superpowers to act," she added.