TOKYO - Japan marked the 78th anniversary of the atomic bombing of its western city of Nagasaki on Wednesday, with the city mayor calling on world leaders to stop relying on nuclear deterrence and move steadily toward abolishing nuclear weapons.

This year's memorial ceremony was significantly scaled down due to severe tropical storm Khanun approaching the region. The ceremony at the Nagasaki Dejima Messe conference center was the first since 1963 to take place indoors rather than at the city's Peace Park close to the hypocenter where the bomb detonated.

At 11:02 am local time, a moment's silence was observed by those attending the ceremony, as this was the time when a US B-29 bomber dropped a plutonium-core atomic bomb, nicknamed Fat Man, on Aug 9, 1945, killing around 74,000 people in Nagasaki by the end of that year.

In his Peace Declaration, Mayor Shiro Suzuki spoke against nuclear deterrence principles. "Now is the time to show courage and make the decision to break free from dependence on nuclear deterrence. I appeal to you to move steadily, along the path to abolishing nuclear weapons through dialogue, not confrontation, based on a concept of security centered on humanity."

The mayor called on the Japanese government, in addition to firmly maintaining the principle of peace stated in the Japanese Constitution, to "engage in diplomatic efforts aimed at disarmament and alleviation of tensions in the region".

UN Secretary-General Antonio Guterres said that "the United Nations will continue working with global leaders to strengthen the global disarmament and non-proliferation regime", in his statement read at the ceremony.

Japan, once a ruthless invader in Asian countries and regions such as China and the Korean Peninsula, has deliberately concealed its ugly history as a perpetrator by repeatedly stressing that it is "the only country that suffered atomic bombings", said Toshiyuki Tanaka, a historian and emeritus professor at Hiroshima City University.

The Japanese government, in its latest defense policy shift marked in the updated security documents, has also triggered grave concerns by vowing to acquire the military power to actively attack its enemy amid military expenditure hikes, seriously deviating from the war-renouncing Article 9 of the Japanese Constitution and the track of a postwar pacifist country.

Japan brutally invaded and occupied many parts of Asia before and during World War II, inflicting untold suffering and heavy casualties on millions of innocent victims.