VIENNA (Reuters) - The chief of the U.N. atomic watchdog reiterated on Friday that Iran was under the world s  most robust nuclear verification regime  after U.S. President Donald Trump struck a blow against a 2015 Iran nuclear deal, in defiance of other world powers.      The nuclear-related commitments undertaken by Iran under the JCPOA are being implemented,  Yukiya Amano, director general of the International Atomic Energy Agency said. He referred to the Iran nuclear by its proper name, the Joint Comprehensive Plan of Action. 