Hiroshima commemorates 72nd anniversary of atomic bombing with a gathering at the city's Peace Memorial Park. (Xinhua/Ma Ping)

This year's ceremony at the Peace Memorial Park near Ground Zero was attended by representatives from 80 countries including the US, the UK, France, and Russia.

Mayor of Hiroshima, Kazumi Matsui, urged the government to "manifest the pacifism in Japan’s Constitution by doing everything in its power to bridge the gap between the nuclear weapon and non-nuclear weapon states, thereby facilitating the ratification of the UN treaty to comprehensively prohibit nuclear weapons.

Prime Minister Shinzo Abe spoke at the ceremony that to truly realize a 'world without nuclear weapons,' the participation of both nuclear weapon states and non-nuclear weapon states is necessary.