Updated at 5:10 a.m. ET
Yukiya Amano, the director general of the International Atomic Energy Agency, has died at age 72, leaving a vacancy at the top of the monitoring body just as tensions over Iran's nuclear ambitions appear to be reaching a critical threshold.
The former Japanese diplomat had led the United Nations' nuclear watchdog since 2009. He was integral to the negotiations leading up to the 2015 nuclear deal with Iran, known as the Joint Comprehensive Plan of Action, or JCPOA. The U.S. unilaterally withdrew from the agreement last year.