UN nuclear watchdog chief Yukiya Amano has died, the International Atomic Energy Agency (IAEA) said on July 22.
"The Secretariat of the International Atomic Energy Agency regrets to inform with deepest sadness of the passing away of Director-General Yukiya Amano," the IAEA secretariat said in a note.
The secretariat did not say how Amano, who was 72, died.
It said Amano was planning to write soon to the Board of Governors announcing his decision to step down in March well before the end of his third four-year term, which ran until November 30, 2021.
The IAEA flag will be lowered to half-staff.
The European Union's foreign policy chief, Federica Mogherini, tweeted July 22 that she was saddened by Amano's death and called him "a man of extraordinary dedication and professionalism."
Amano had held the position of IAEA director-general since 2009, taking over from Muhammad ElBaradei and steering the UN agency through a period of intense diplomacy over Iran's nuclear program.
The IAEA announced last September that Amano had undergone an unspecified medical procedure. He had appeared increasingly frail in every recent public appearance.
The note did not lay out a time frame for naming his successor.
Argentina's ambassador to the IAEA, Rafael Grossi, is running to succeed Amano, and diplomats say the agency's Chief Coordinator Cornel Feruta of Romania, effectively Amano's chief of staff, is likely to run.