The historic - though largely symbolic - treaty will apply from January 2021. Nuclear powers US, Russia, China, UK and France have not signed.
The United Nations announced on Saturday that 50 countries have ratified a UN treaty to ban nuclear weapons triggering its entry into force in 90 days, a move hailed by anti-nuclear activists but strongly opposed by the United States and the other major nuclear powers.
As of Friday, the treaty had 49 signatories, and the United Nations said the 50th ratification from Honduras had been received.
UN Secretary-General António Guterres commended the 50 states and saluted "the instrumental work" of civil society in facilitating negotiations and pushing for ratification, UN spokesman Stephane Dujarric said.
The UN chief said the treaty’s entry into force on January 22, 2021, culminates a worldwide movement "to draw attention to the catastrophic humanitarian consequences of any use of nuclear weapons" and "is a tribute to the survivors of nuclear explosions and tests, many of whom advocated for this treaty," he said.
Guterres said the treaty "represents a meaningful commitment towards the total elimination of nuclear weapons, which remains the highest disarmament priority of the United Nations," Dujarric said.
Beatrice Fihn, executive director of the International Campaign to Abolish Nuclear Weapons, the 2017 Nobel Peace Prize-winning coalition whose work helped spearhead the nuclear ban treaty, said: "This moment has been 75 years coming since the horrific attacks on Hiroshima and Nagasaki, and the founding of the UN which made nuclear disarmament a cornerstone."
"The 50 countries that ratify this Treaty are showing true leadership in setting a new international norm that nuclear weapons are not just immoral but illegal," she said.
The 50th ratification came on the 75th anniversary of the ratification of the UN Charter which officially established the United Nations and is celebrated as UN Day.
"The United Nations was formed to promote peace with a goal of the abolition of nuclear weapons," Fihn said. "This treaty is the UN at its best — working closely with civil society to bring democracy to disarmament."
The treaty requires that all ratifying countries "never under any circumstances... develop, test, produce, manufacture, otherwise acquire, possess or stockpile nuclear weapons or other nuclear explosive devices."
It also bans any transfer or use of nuclear weapons or nuclear explosive devices - and the threat to use such weapons - and requires parties to promote the treaty to other countries.
Once it enters into force all countries that have ratified it will be bound by those requirements.
The United States had written to treaty signatories saying the Trump administration believes they made "a strategic error" and urged them to rescind their ratification.
The US letter, obtained by The Associated Press, said the five original nuclear powers - the US, Russia, China, Britain and France - and America’s NATO allies "stand unified in our opposition to the potential repercussions" of the treaty.
It says the Treaty on the Prohibition of Nuclear Weapons, known as the TPNW, "turns back the clock on verification and disarmament and is dangerous" to the half-century-old Nuclear Non-proliferation Treaty, considered the cornerstone of global nonproliferation efforts.
"The TPNW is and will remain divisive in the international community and risk further entrenching divisions in existing nonproliferation and disarmament fora that offer the only realistic prospect for consensus-based progress," the letter said. "It would be unfortunate if the TPNW were allowed to derail our ability to work together to address pressing proliferation."
Fihn has stressed that "the non-proliferation Treaty is about preventing the spread of nuclear weapons and eliminating nuclear weapons, and this treaty implements that. There’s no way you can undermine the Non-proliferation Treaty by banning nuclear weapons. It’s the end goal of the Non-proliferation Treaty."
"Nobody needs nuclear weapons"
The NPT sought to prevent the spread of nuclear arms beyond the five original weapons powers. It requires non-nuclear signatory nations to not pursue atomic weapons in exchange for a commitment by the five powers to move toward nuclear disarmament and to guarantee non-nuclear states’ access to peaceful nuclear technology for producing energy.
Rebecca Johnson, a co-founder and first president of the International Campaign to Ban Nuclear Weapons, said: "The ban treaty is as much about just making it much more possible for people all around the world to see nobody needs nuclear weapons, and they’re actually an impediment, an obstacle - they’re in the way of dealing with the real security threats we have on the ground from COVID to climate."
She said in an AP interview that nuclear weapons can’t prevent or deal with conflicts. "They’re just in the way, and they’re highly expensive, and the governments that have them are distracted from the real security issues by trying to constantly pay for these arms races that they’re still obsessed with."
Francesco Rocca, president of the International Federation of Red Cross and Red Crescent Societies, said: "The simple reality is that the international community could never hope to deal with the consequences of a nuclear confrontation. No nation is prepared to deal with a nuclear confrontation. What we cannot prepare for, we must prevent."
There are over 14,000 nuclear bombs in the world, thousands of which are ready to be launched in an instant, Rocca said. The power of many of those warheads is tens of times greater than the weapons dropped on Nagasaki and Hiroshima.
The treaty was approved by the 193-member UN General Assembly on July 7, 2017, by a vote of 122 in favour, the Netherlands opposed, and Singapore abstaining. Among countries voting in favour was Iran. The five nuclear powers and four other countries known or believed to possess nuclear weapons — India, Pakistan, North Korea and Israel — boycotted negotiations and the vote on the treaty, along with many of their allies.
Setsuko Thurlow, a survivor of the 1945 bombing of Hiroshima, who has been an ardent campaigner for the treaty, said: "When I learned that we reached our 50th ratification, I was not able to stand."
"I remained in my chair and put my head in my hands and I cried tears of joy," she said in a statement. "I have committed my life to the abolition of nuclear weapons. I have nothing but gratitude for all who have worked for the success of our treaty."