TOKYO, Aug. 9 (Xinhua) -- Nagasaki City in Japan commemorated the 73rd anniversary of the U.S. atomic bombing on Thursday, with its mayor urging the Japanese government to support an international nuclear ban treaty which came into effect last year.

"I hereby ask that the government of Japan, the only country to have suffered from the wartime use of nuclear weapons, support the Treaty on the Prohibition of Nuclear Weapons and fulfill its moral obligation to lead the world towards denuclearization," Mayor of Nagasaki Tomihisa Taue said in his peace declaration.

U.N. Secretary General Antonio Guterres by attending the commemorative event and observations became the first sitting chief of the international body to attend the ceremony which is held every year, with the peace declaration also calling on global leaders to eliminate nuclear weapons.

The declaration urged global leaders to remember "the resolve" of the first U.N. General Assembly resolution to aim for the elimination of nuclear arsenals.

"To the great concern of those in the atomic-bombed cities, a shift towards openly asserting that nuclear weapons are necessary and that their use could lead to increased military might is once again on the rise," the declaration also said.

At 11:02 a.m. local time, a moment's silence was observed by those attending the ceremony as this was the time when a U.S. B-29 bomber dropped a plutonium-core atomic bomb, nicknamed "Fat Man," killing around 74,000 people in Nagasaki by the end of that year.

The atomic bombing of Nagasaki follows one dropped on Hiroshima on Aug. 6, with both bombings a means of accelerating the end of World War II and forcing Japan to surrender without a land invasion that would have claimed many, many more lives as experts attest.

Taue went on to say that the two atomic bombed cities of Hiroshima and Nagasaki have high hopes for "irreversible denuclearization."

The mayor urged the Japanese government to use the opportunity to create a nuclear-free zone in Northeast Asia.

Guterres, in his speech, meanwhile, called on all nations to commit to nuclear disarmament and urgently make "visible" progress.

"Disarmament processes have slowed and even come to a halt," Guterres said, intimating that the adoption last year of the Treaty on the Prohibition of Nuclear Weapons had shown the frustration that many countries had been feeling.

Japanese Prime Minister Shinzo Abe, for his part, said in his speech that "in recent years, differences in the approaches of various countries on nuclear disarmament have become evident."

He went on to say that Japan will serve as a bridge between nuclear powers and non-nuclear states, and that "an accurate understanding of the tragic realities of the atomic bombings and cooperation from both parties is essential."