Flanked by French Deputy Representative to the United Nations Alexis Lamek (L) and British Representative to the United Nations Matthew Rycroft (R), U.S. Ambassador to the United Nation Nikki Haley speaks Monday to reporters at the United Nations headquarters in New York on a nuclear weapons ban treaty, which the U.S., Britain and France oppose. (Drew Angerer/Getty Images)

The United States, Britain, France and other major powers protested on Monday as the United Nations began work on what backers said would be a binding prohibition on nuclear weapons.

Russia and China also sat out the opening General Assembly session. Russia had voted against launching the effort last fall. China abstained.

The proposed ban, backed by Pope Francis, U.N. Secretary General António Guterres and dozens of humanitarian and nonproliferation groups, sets most of the major nuclear powers against more than 100 smaller non-nuclear states who seek a treaty this year.

“As a mom, as a daughter, there is nothing I want more for my family than a world that has no nuclear weapons,” said Nikki Haley, the U.S. ambassador to the U.N. “But we have to be realistic. Is there anyone who believes that North Korea would agree” to give up its nuclear weapons on the U.N.’s orders?

She and representatives from Britain and France spoke to reporters as the U.N. General Assembly began discussion on the issue. More than 30 nations sat out the first session, many at U.S. urging, in support of the argument that a blanket ban now is impractical or dangerous.

“Is it any surprise that Iran is supportive of this?” Haley asked. “It is not.”

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North Korea developed nuclear weapons through a rogue program and is attempting to field a long-range missile that could deliver a weapon to U.S. shores, according to U.S. officials. It can already target U.S. forces and allies in Asia, they have said.

Iran denies it sought a nuclear weapon, but agreed to curtail its nuclear program in an international deal led by former president Barack Obama and heavily criticized by President Trump.

Although Obama had set the eventual eradication of nuclear weapons as a goal, his administration also opposed a U.N. ban.

The Trump administration has not yet said whether it will affirm the long-range goal of eliminating nuclear weapons or pledge to further shrink the U.S. arsenal. The White House is conducting a new nuclear posture review expected to take a year or more.

Haley said Monday that the United States and other major powers boycotting the U.N. discussion “believe in” the Nuclear Non-Proliferation Treaty. The landmark treaty that took effect in 1970 commits nations with nuclear weapons to move toward disarmament while prohibiting non-nuclear states from obtaining the weapons. Signers of the treaty also agree that all nations may have access to nuclear power and other peaceful uses of nuclear technology.

As a presidential candidate, Trump suggested that U.S. allies Japan and South Korea could develop nuclear weapons and defend themselves, instead of relying on the U.S. nuclear umbrella, and suggested that nuclear weapons could be effective against Islamic State militants. He said both that he wanted the United States to have an up-to-date and perhaps expanded nuclear arsenal, and that he would like to see a nuclear-free world.

At the General Assembly session Monday, diplomats said they would pursue a draft document this spring. A model is the two-decade-old U.N.-backed ban on land mines, which is credited with reducing use of those weapons even though major nations including then United States, Russia and China have declined to sign it.

Toshiki Fujimori , a baby when he survived the 1945 U.S. nuclear bomb attack on Hiroshima, Japan, addressed the opening session.

“Everybody thought I would die, yet I survived. It’s a miracle,” Fujimori said. “I am here at the U.N. asking for the abolition of nuclear weapons. . . . This is the mission I am given as a survivor.”

It faces a steep hurdle. The U.N. Security Council’s five permanent members — who hold veto power — are the five original big nuclear powers: The United States, United Kingdom, France, Russia and China.

“The U.K. 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,” British U.N. Ambassador Matthew Rycroft said Monday. “They cannot and will not work.”