The International Atomic Energy Agency announced on Monday that its director general, Yukiya Amano, has died. He was 72.
The UN nuclear watchdog said in an announcement that it regrets to inform with deepest sadness of the passing away of Amano.
The announcement shared a letter Amano wrote to the Board of Governors revealing his decision to step down.
In the letter, Amano said that during the past decade, the agency delivered concrete results to achieve its objective of atoms for peace and development.
Amano became IAEA chief in December 2009 after stressing that he is from the only country in the world to have suffered atomic bombings.
He was serving a third term which was scheduled to end in 2021.
Amano spearheaded efforts to strengthen the safety of nuclear power plants following the 2011 accident at Fukushima Daiichi in northeastern Japan.
He also worked to restrict Iran's nuclear program after Tehran signed a deal in 2015 with five world powers through inspections of Iran's nuclear facilities.
Amano also set up a team of experts to prepare for the resumption of IAEA inspections in North Korea.
In an interview with NHK in April, Amano said steadfast inspections ensure that an agreement will last for a long time and will benefit North Korea, the countries concerned, and the international community.
He also said that the IAEA is preparing itself to visit North Korea when an agreement is reached between these nations.
Amano had been in poor health since last year and had been absent from board meetings to undergo treatment.