Nagasaki is marking the 73rd anniversary of the atomic bombing over the city, joined by the head of the United Nations for the first time amid the effort to push forward North Korea's denuclearization.

UN Secretary-General Antonio Guterres urged all countries to commit to nuclear disarmament and to take concrete steps as he raised concerns about the slowing effort. He said fears of nuclear war are still present 73 years after the Nagasaki and Hiroshima bombings and that they should never be repeated.

Nagasaki Mayor Tomihisa Taue urged Japan's government to do more to lead nuclear disarmament around the world.

The bombing of Nagasaki on August 9, 1945, was the second US nuclear attack on Japan, killing 70,000 people, three days after the bomb dropped on Hiroshima killed 140,000.