HIROSHIMA – Hiroshima on Sunday marked the 72nd anniversary of its atomic bombing by the U.S., with Mayor Kazumi Matsui using the annual memorial ceremony to call on the central government to help make a treaty banning nuclear weapons a reality.

This year’s ceremony at Peace Memorial Park near ground zero follows the adoption by 122 U.N. members last month of the world’s first treaty to comprehensively ban nuclear weapons.

The treaty’s preamble uses the term hibakusha in mentioning “the unacceptable suffering” experienced by the survivors of the Hiroshima and Nagasaki A-bombings, which had killed an estimated 214,000 people by the end of 1945.

But Japan — together with the world’s nuclear weapon states and other countries under the U.S. nuclear umbrella — refused to participate in the U.N. treaty.

In the city’s annual Peace Declaration, Matsui stopped short of demanding that Japan join the treaty, but urged the government to “manifest the pacifism in our Constitution by doing everything in its power to bridge the gap between the nuclear weapon and non-nuclear weapon states, thereby facilitating the ratification.”

He said the countries that adopted the treaty “demonstrated their unequivocal determination to achieve abolition,” and that now is the time for all governments to “strive to advance further toward a nuclear weapon-free world.”

Prime Minister Shinzo Abe avoided any mention of the U.N. nuclear weapons ban treaty in his speech at the ceremony.

“For us to truly realize a ‘world without nuclear weapons,’ the participation of both nuclear weapon states and non-nuclear weapon states is necessary,” he said.

Later in the day, after meeting with representatives of seven local hibakusha groups who protested Japan’s refusal to participate in the U.N. treaty, Abe defended the decision to stay out, saying “a realistic approach” is needed to reach the goal of having a world without nuclear weapons.

“We think (the treaty) must not result in the distance between the nuclear weapon and non-nuclear weapon states being further widened and the realization of a world without nuclear weapons getting further away,” Abe said at a news conference.

“By firmly maintaining our three non-nuclear principles and continuing to appeal to both sides, Japan is determined to lead the international community,” Abe said in his speech, referring to the government’s policy of not producing, possessing or allowing nuclear weapons on its territory.

At the news conference, however, Abe said he did not see any need to turn the three-point policy into law.

About 50,000 people came to the park for the ceremony, at which 80 nations plus the European Union were represented.

Nuclear states Britain, France, the United States and Russia sent representatives, as did India, Israel and Pakistan, which are also known to possess atomic weapons.

U.N. Secretary-General Antonio Guterres called for all states to work toward a world free of nuclear weapons “in their own ways,” in a message read on his behalf by Izumi Nakamitsu, U.N. undersecretary-general and high representative for disarmament affairs.

“Hiroshima’s message of peace and the heroic efforts of hibakushas have reminded the world of the devastating humanitarian consequences of nuclear weapons. … The United Nations stands with you in our shared pursuit of a world free of nuclear weapons,” the message said.

A moment of silence was observed at 8:15 a.m., when the atomic bomb dubbed “Little Boy” exploded about 600 meters above Hiroshima on Aug. 6, 1945, leaving an estimated 140,000 people dead by the end of the year.

A second atomic bomb was dropped on Nagasaki on Aug. 9 and Japan surrendered six days later, bringing an end to World War II.

Matsui demanded in his speech that the government give more compassionate assistance to elder hibakusha, as well as to “the many others also suffering mentally and physically from the effects of radiation.”

City officials said “the many others” reference includes people affected by the March 2011 triple core meltdown at the Fukushima No. 1 nuclear power plant.

This year’s anniversary is the first to follow the election of U.S. President Donald Trump, whose predecessor, Barack Obama, last year became the first sitting U.S. leader to visit Hiroshima. Trump had suggested before his election that Japan and South Korea should acquire nuclear weapons in the future, and U.S. Secretary of State Rex Tillerson refused to rule this out in a U.S. interview in March.

Braving high temperatures from the early morning, young and old visited the park ahead of the ceremony to pay their respects to those who died in the bombing and offer prayers for peace.

Hiroshima native Masaharu Masuda, 70, offered a prayer as he does every year in memory of his parents, who both experienced the bombing. The midsummer heat reminded him of how his older sister always wore long sleeves when they were younger to hide the keloid scars on her arms.

Masuda said he is disappointed by the Japanese government’s “half-hearted” response to the nuclear ban treaty, and worries that the world is losing interest in Hiroshima’s message.

“People used to say with feeling, ‘No more Hiroshimas,’ but I hear it less and less these days,” he said.

Naomi Miyamoto, 56, came from Tokyo to place flowers at the memorial and renew his commitment to peace and nuclear abolition.

“I don’t have confidence that the way Japan and other countries deal with each other will change any time soon, but one thing individual people can do is educate themselves about what happened here in Hiroshima,” he said.