The head of the UN's nuclear watchdog, Yukiya Amano, 天野 之弥, has died at the age of 72, the agency said in a statement.
He has led the International Atomic Energy Agency (IAEA) since 2009, and was due to step down in March because of an unspecified illness.
During his tenure he had overseen a period of tense negotiations regarding Iran's nuclear programme.
It is not yet clear who will succeed him, though discussions over who will replace him began last week.