“This prize is a tribute to the tireless efforts of many millions of campaigners and concerned citizens worldwide who, ever since the dawn of the atomic age, have loudly protested nuclear weapons, insisting that they can serve no legitimate purpose and must be forever banished from the face of our earth,” ICAN said in a statement.
The United States, which with Russia has the biggest stockpile of nuclear weapons, had said the treaty would do nothing to alleviate the possibility of nuclear conflict and might even increase it.
The committee acknowledged the view held by nuclear-armed countries in its statement, noting that “an international legal prohibition will not in itself eliminate a single nuclear weapon, and that so far neither the states that already have nuclear weapons nor their closest allies support the nuclear weapon ban treaty.”
Despite those admonitions, at least 53 member states of the United Nations have signed the treaty since a ceremony to start the ratification process was held at the General Assembly on Sept. 20. While only three — Guyana, the Vatican and Thailand — had formally ratified the treaty as of Friday, others are expected to do so in the coming year.
The treaty will go into effect 90 days after 50 United Nations member states have formally ratified it.
Delegates representing two-thirds of the General Assembly’s 193 members participated in the treaty negotiations.
“We have received this news with so much joy,” Elayne Whyte Gómez, the Costa Rican ambassador to the United Nations in Geneva, who was the chairwoman of the negotiations, said in a telephone interview. “Every year there should be at least one happy event to give us hope, and this was it.”
She said ICAN’s work “represented efforts by civil society activists who approached governments around the world and maintained the momentum of the negotiations to keep them going.”
The prize came as a surprise to Beatrice Fihn, the executive director of ICAN, which has a three-person office in Geneva. She said at a news conference that she had thought at first that the congratulatory telephone call from the Nobel committee was fake.
Under the agreement, all nuclear weapons use, threat of use, testing, development, production, possession, transfer and stationing in a different country are prohibited.
For nuclear-armed nations that choose to join, the treaty outlines a process for destroying stockpiles and enforcing the countries’ promise to remain free of nuclear weapons.
“I don’t think we have unrealistic expectations that tomorrow nuclear weapons will be gone,” Ms. Fihn said. “But I think this is really a moment to be really inspired that it is possible to do something.”
The prize came against the backdrop of the most serious worries about a possible nuclear conflict since the Cold War, punctuated by a bellicose standoff between the United States and North Korea.
The North Korean leader, Kim Jong-un, has defied United Nations sanctions prohibiting his isolated country’s repeated nuclear weapons and missile testing, and has threatened to strike the American heartland with the “nuclear sword of justice.”
President Trump, who has mocked Mr. Kim by calling him “Little Rocket Man,” has said he would have no choice but to “totally destroy” North Korea if the United States or its allies are attacked.
Berit Reiss-Andersen, chairwoman of the Norwegian Nobel Committee, told reporters that the award was not intended to send a message directly to Mr. Trump. “We’re not kicking anyone in the legs with this prize,” she said. The committee instead intended to give “encouragement to all players in the field” to disarm.
Ms. Fihn was more direct in her appraisal of the Kim-Trump standoff and the anxieties it has raised. “Nuclear weapons do not bring stability and security” she told reporters. “We can see that right now.”
There was no immediate reaction to the prize from the Trump administration or from North Korea. But in Moscow, Dmitri S. Peskov, a spokesman for President Vladimir V. Putin of Russia, told reporters that “there is no alternative” to nuclear parity to maintain world stability.
Jens Stoltenberg, the secretary-general of NATO, who has strongly criticized the nuclear weapons treaty, said in a statement quoted by news agencies that he welcomed “the attention given to the issue” of nuclear weapons by the Nobel committee’s choice, but he reiterated his view that the treaty had put years of nonproliferation efforts at risk.
Proponents of the treaty have said that they never expected any nuclear-armed country would sign it right away. But they argued that the treaty’s widespread acceptance elsewhere would increase the public pressure and stigma of possessing nuclear weapons.
The same strategy was used by proponents of the treaties that banned chemical and biological weapons, land mines and cluster bombs.
Nuclear weapons have defied attempts to contain their proliferation since the United States dropped two atomic bombs on Japan in 1945, which led to Japan’s surrender and the end of World War II.
The destruction wrought by those weapons laid the foundation for the nuclear arms race and the doctrine of deterrence, which holds that mutually assured destruction of nuclear-armed antagonists is the only way to prevent an attack.
Besides North Korea, Russia and the United States, the other nuclear-armed states are Britain, China, France, India, Pakistan and Israel.
The United States had leaned hard on its allies, especially non-nuclear powers, to boycott the treaty talks that began at the United Nations earlier this year.
Russia and China are equally opposed to the efforts to ban nuclear weapons through an international treaty.
But on this issue, the naysayers are in the clear minority.
The United States was also isolated in 1997, when the Nobel Peace Prize was awarded to a civil society group that pushed to abolish land mines — the International Campaign to Ban Landmines and its coordinator, Jody Williams.
The international agreement that her group pushed for, the Convention on the Prohibition of the Use, Stockpiling, Production and Transfer of Anti-Personnel Mines and on their Destruction, known simply as the Mine Ban Treaty, has been signed by more than three-fourths of all countries around the world. The United States, Russia and China remain outliers.
It is unusual for organizations to receive the prize. Others have included the International Committee of the Red Cross and the Office of the United Nations High Commissioner for Refugees.
Who won the 2016 Nobel Peace Prize?
■ President Juan Manuel Santos of Colombia was honored for pursuing a deal to end 52 years of conflict with the leftist rebel group known as the Revolutionary Armed Forces of Colombia, the longest-running war in the Americas, just five days after Colombians rejected the agreement in a shocking referendum result.