A U.N. treaty banning nuclear weapons entered into force Friday with at least 50 signatories having completed their ratification processes by last October, a long-awaited development for atomic bomb survivors and anti-nuclear activists.

While participating countries and regions hope that the Treaty on the Prohibition of Nuclear Weapons will provide a boost for the global nuclear disarmament movement, the launch of the historic international agreement has been marred by the absence of nuclear weapons states as well as Japan, the only country that has suffered the devastation of atomic bombings.

Photo shows one of the U.S. thermonuclear tests that began in March 1954 at Bikini Atoll in the Pacific. (Getty/Kyodo)

It is the first pact prohibiting the development, testing, possession and use of nuclear weapons, although the Nuclear Non-Proliferation Treaty, which took effect in 1970, serves as a broader platform at the United Nations where over 190 countries and regions including nuclear weapons states discuss ways to promote nuclear disarmament.

Currently, 51 countries and regions have ratified the treaty, including Austria, Malaysia, Mexico, New Zealand and South Africa.

U.N. Secretary General Antonio Guterres hailed the launch of the new treaty, saying it is "an important step toward the goal of a world free of nuclear weapons and a strong demonstration of support for multilateral approaches to nuclear disarmament."

"The survivors of nuclear explosions and nuclear tests offered tragic testimonies and were a moral force behind the Treaty. Entry into force is a tribute to their enduring advocacy," he added in his video statement.

The symbolism of the treaty is significant as it was realized more than 75 years after the advent of nuclear weapons, with the world having witnessed their horrific human toll.

Austrian Foreign Minister Alexander Schallenberg has praised the determination of survivors of the U.S. atomic bombings of Hiroshima and Nagasaki.

"Without them, without the struggle they have conducted for the last 75 years, this (treaty) would not have been possible," he said in an exclusive interview with Kyodo News earlier this week.

Schallenberg added that he would welcome their attendance at the first conference of state parties to be held in Vienna at the end of this year at the earliest.

"It would be a very strong signal to hold a conference in Hiroshima or Nagasaki" in the future, although the decision ultimately rests with the Japanese government, he said.

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The effectiveness of the accord, however, appears in question as it lacks the legal authority to require nuclear powers to eliminate their arsenals.

The five permanent members of the U.N. Security Council -- Britain, China, France, Russia and the United States, all of which are nuclear powers -- are opposed to the treaty. Other countries that possess nuclear weapons, such as India, Israel, North Korea and Pakistan, have also declined to join.

While nuclear powers often speak of the importance of promoting nuclear arms control or disarmament, they maintain a huge number of the weapons, with the United States and Russia possessing especially large arsenals.

The 2010 New Strategic Arms Reduction Treaty, which is set to expire in February, is now the only arms control pact between Washington and Moscow.

It caps strategic nuclear warheads at 1,550 each and curbs the number of intercontinental ballistic missiles and bombers that deliver them to 800.

The administration of former President Donald Trump had been reluctant to renew the accord, saying a new framework involving China would be necessary, while Russia has been seeking to extend the pact.

In a more reconciliatory move, the new administration of President Joe Biden said Thursday that it intends to seek a five-year extension with Russia.

The Trump administration also pulled the United States out of the 1987 Intermediate-Range Nuclear Forces Treaty with Russia in August 2019, leaving the two countries no longer constrained in their deployment of shorter-range land-based nuclear weapons.

Japan, which took the lead in the adoption of a U.N. resolution calling for the total elimination of nuclear arms for the 27th consecutive year, has decided not to sign the nuclear ban treaty in consideration of its security ties with the United States.

Protected by the so-called U.S. nuclear umbrella against security threats from North Korea and others, the Japanese government has held firm in distancing itself from the antinuclear pact, despite repeated calls from survivors of the U.S. atomic bombings to join the accord.

"It is utter negligence that Japan, the only country in the world to suffer nuclear bombing, is turning a blind eye," said Miyako Jodai, 81, a survivor who speaks publicly about her experience of the atomic bombing of Nagasaki.

Prime Minister Yoshihide Suga said Friday that while Japan has no intention of joining the treaty, it would continue efforts to "build a bridge" between nuclear weapons states and non-nuclear weapons states, including by telling the world of the horrific consequences of using nuclear weapons.

The nuclear ban treaty, adopted in 2017, took effect 90 days after its ratification by 50 countries.