Hiroshima, Japan - As tens of thousands of people gathered in the city of Hiroshima in western Japan on Sunday to commemorate the 78th anniversary of the US atomic bomb attack there, officials urged a re-think of the theory of nuclear deterrence.

Some 50,000 participants, including survivors and their descendants, observed a minute’s silence in the Peace Memorial Park near ground zero at 8:15 AM, the moment when a US B-29 bomber dropped an atomic bomb on the city 78 years ago in the closing days of World War II.

In his Peace Declaration delivered at the ceremony, Hiroshima Mayor Kazumi Matsui urged world leaders to abandon the theory of nuclear deterrence.

"Leaders around the world must confront the reality that nuclear threats now being voiced by certain policymakers reveal the folly of nuclear deterrence theory," Matsui said.

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"It will be increasingly important for us to urge policymakers to abandon nuclear deterrence in favor of a peaceful world that refuses to compromise individual dignity and security."

In a statement read out at the ceremony, UN Secretary-General António Guterres said the only way to eliminate the nuclear risk would be to abolish nuclear weapons.

In a tweet sent on the platform X formerly known as Twitter, Guterres said: "I stand with the people of Hiroshima (...) working tirelessly to ensure that nuclear weapons are never used again."

Japan's Prime Minister Fumio Kishida, who is from Hiroshima and attended the ceremony, said in his speech: "At present, the road to nuclear disarmament has become even more difficult as the division of the international community over nuclear disarmament and nuclear threats from Russia deepened."

"But especially under these circumstances, it is important to revive the international momentum for the realization of a world without nuclear weapons," Kishida added.

The unprecedented nuclear attack in 1945 killed tens of thousands of residents in seconds, and by the end of that year, some 140,000 had died due to the bombing.

The United States dropped a second atomic bomb three days later on Nagasaki on the island of Kyushu. On August 15, 1945, Japan surrendered to Allied Forces, bringing the war to an end.

The United States government still has not apologized for the nuclear attacks.

Officials in Nagasaki in southwestern Japan announced on Sunday that the commemoration ceremony there on Wednesday this week will not be held in the Peace Park as usual, but indoors because of the approaching Typhoon Khanun. It is the first time since 1963 that it will not take place outdoors.