UN nuclear watchdog chief Yukiya Amano has died, the International Atomic Energy Agency (IAEA) said on Monday. The news came as the 72-year-old Japanese was preparing to step down because of an unspecified illness, Reuters reports.

Amano held the position of IAEA director general since 2009 and steered the UN agency through a period of intense diplomacy over Iran’s nuclear program.

He had been preparing to leave his position in March, well before the end of his third four-year term, which ran until November 30, 2021.

A race to succeed Amano had been taking shape since last week, when it became clear he would step down early.