Abe also noted that people have an obligation to continue telling future generations about the inhumane nature of nuclear weapons.
"If the human family forgets history or stops confronting it, we could again commit a awful error", Matsui said at the event on Monday.
"Atom bombs were dropped on Hiroshima and Nagasaki on August 6 and 9, 1945 respectively, which wreaked havoc of unimaginable dimensions".
But as with years past and, perhaps, for those in the future, while Japan has a tendency to focus exclusively on the inward tragedy that nuclear and chemical warfare has inflicted on it, many experts on the matter hope that Japan will also take the time to remember that its own involvements in World War II had also brought immeasurable suffering. Tokyo is under the protection of the U.S.'s so-called "nuclear umbrella" and is not a signatory of Treaty on the Prohibition of Nuclear Weapons. "I want Japan to work toward eliminating nuclear weapons", Ota added.
But reports suggest Tokyo is considering a summit soon between Kim and Prime Minister Shinzo Abe, with local media floating a possible meeting on the sidelines of an global forum in Russia's Vladivostok next month.
The anniversary comes amid hopes to denuclearise North Korea after its pledge to do so at the Singapore summit in June.
"Ultimately, I myself will have to directly face chairman Kim Jong Un and engage in dialogue and resolve the nuclear, missile and, above all, the all-important abduction issue, and then build new Japan-North Korea relations", Abe said in Hiroshima on Monday.
Prime Minister Shinzo Abe says Japan is determined to lead efforts to bridge deepening rifts between countries that possess nuclear weapons and those that do not.
"In recent years, it has become evident that gaps exist among countries about ways to proceed with nuclear arms reduction", Abe told the ceremony, without directly referring to the treaty.
The final death toll is estimated at 140,000 and - along with the bomb that was dropped on Nagasaki three days later - ended Japan's involvement in the Second World War.
Organizers of this year's observance hope to draw attention to the treaty and have the U.S.be the first of the nuclear powers to take the first steps in ratifying it. In order to gain cooperation from both sides, it is important for everyone to understand "the reality of the tragedy of nuclear attacks, " he said, and reiterated Japan's pledge to maintain it pacifist and non-nuclear principles.
Barack Obama became the first sitting USA president to visit Hiroshima in May 2016.