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, a 72-year-old former Japanese diplomat, 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 announced last September that Amano had undergone an unspecified medical procedure. He had appeared increasingly frail in every recent public appearance.
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.
Amano oversaw the signing of a landmark nuclear agreement between Iran and six major powers -- Britain, China, France, Germany, Russia and the United States. The 2015 accord provided Iran with relief from sanctions in return for curbs on its nuclear program.
U.S. President Donald Trump last year withdrew the United States from the agreement and reimposed economically crippling sanctions in many sectors, including the crucial oil and financial industries.
Jackie Wolcott, the U.S. ambassador to international organizations in Vienna, has expressed her "deepest condolences...upon the sad news" of Amano's death.
"The United States and all nuclear nonproliferation advocates have lost a great friend, and the United Nations family has lost an exceptional public servant," Wolcott said in a statement.
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."
So saddened by the loss of @iaeaorg DG #Amano A man of extraordinary dedication & professionalism, always at the service of the global community in the most impartial way. I’ll never forget the work done together. It has been for me a great pleasure & privilege working with him
— Federica Mogherini (@FedericaMog) July 22, 2019
Iranian Deputy Foreign Minister Abbas Araghchi paid tribute to Amano on Twitter.
"My deep condolences.... We worked very closely," tweeted Araghchi, who took part in the negotiations for the 2015 nuclear deal.
"I commend his skillful and professional performance...[that] resulted in complete closure" of the nuclear accord.
France, Germany, and Britain -- three of the six remaining accord signatories -- have tried to salvage the deal and have proposed a complicated financial barter system designed to provide some economic relief to Tehran.
The IAEA statement 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.
The IAEA flag will be lowered to half-staff.