TOKYO – The Japanese city of Nagasaki on Sunday marked the 75th anniversary of the U.S. atomic bombing, with the mayor and dwindling survivors urging world leaders including their own to do more for a nuclear weapons ban.

At 11:02 a.m., the moment the B-29 bomber Bockscar dropped a 4.5-ton plutonium bomb dubbed "Fat Man," Nagasaki survivors and other participants stood in a minute of silence to honor more than 70,000 dead.

The Aug. 9, 1945, bombing came three days after the U.S. dropped its first atomic bomb on Hiroshima, the world's first ever nuclear attack that killed 140,000. On Aug. 15, Japan surrendered, ending World War II.

At the event at Nagasaki Peace Park, scaled down because of the pandemic, Mayor Tomihisa Taue read a peace declaration in which he raised concern that nuclear states had in recent years retreated from disarmament efforts. Instead, they are upgrading and miniaturizing nuclear weapons for easier use, he said. Taue singled out the U.S. and Russia for increasing risks by scrapping the Intermediate-range Nuclear Forces Treaty.

"As a result, the threat of nuclear weapons being used is increasingly becoming real," Taue said. Noting that the Nuclear Proliferation Treaty entered into force 50 years ago, Taue urged the U.S. and Russia to show a workable way toward their nuclear disarmament.

He said that "the true horror of nuclear weapons has not yet been adequately conveyed to the world at large" despite struggle and efforts by hibakusha, or atomic bombing survivors, to make Nagasaki the tragedy's last place.

He also urged Japan's government and lawmakers to quickly sign the 2017 Treaty on the Prohibition of Nuclear Weapons.

An aging group of survivors have expressed a growing sense of urgency to tell their stories in hopes of reaching younger generations to continue their effort toward establishing a nuclear-free world.

"There is not much time left for us survivors," said Shigemi Fukabori, 89. He was a 14-year-old student mobilized to work at a shipyard when Nagasaki was bombed. "I'm determined to keep telling my story so that Nagasaki will be the last place on Earth to have suffered an atomic attack."

Fukabori, who instantly lost four siblings, said he never forgets the pile of charred bodies, bombed-out streetcars and the badly injured desperately asking for help and water as he rushed back to his house in the back of the Urakami Cathedral, which was also nearly destroyed. "We don't want anyone else to have to go through this," he said.

"Nagasaki bears a responsibility as a witness of catastrophic results the nuclear weapon caused to humanity and environment," Fukabori said in his speech at the ceremony, representing the Nagasaki survivors. "I hope as many people as possible to join us, especially the young generations to inherit our baton of peace and keep running."