A new top inspector took charge Tuesday of the International Atomic Energy Agency as it faces one of the most turbulent periods in its 52-year history. Yukiya Amano, 62, is a career diplomat and lawyer who served as Japan's representative to the agency until his selection as director general in July. He inherits crises with Iran and North Korea, as well as the weakening of the global security system meant to curtail the spread of nuclear weapons. Mahmoud Ahmadinejad, Iran's president, greeted Amano's first day in office with a defiant threat. 'Friendly relations with the agency are over,' he told a television interviewer in Iran late Tuesday. He also declared that Tehran had no duty to tell the U.N. agency about its plans to build nuclear sites unless it used imported technology. No such rule exists. But if Ahmadinejad meant that Iran would tell the IAEA nothing about the plans it announced Sunday for building 10 enrichment plants, that silence would pose a major diplomatic test of Amano's short tenure. Amano seemed to anticipate Ahmadinjad's remarks when he spoke to staff members in Vienna earlier on Tuesday at the outset of his four-year term. 'The situation surrounding the agency is stormy now,' he said, according to a statement posted on the nuclear agency's Web site. 'We have a lot of difficult challenges, but I would like to do my best.' He pledged to fight the proliferation of nuclear arms, to enhance nuclear security and to provide a sound basis for nuclear energy. 'I will try to be an impartial, reliable and professional director general,' he added. Amano is the first Asian to lead the agency and comes from the only nation ever attacked with nuclear arms. Born two years after the end of World War II, he grew up as his country wrestled with the nuclear destruction of Hiroshima and Nagasaki. After being elected in July, he alluded to that experience and pledged to work hard to battle nuclear proliferation. 'As a national coming from Japan,' he said, 'I'll do my utmost to prevent the spread of nuclear weapons.' He has extensive experience in disarmament and nonproliferation diplomacy, as well as issues involving nuclear energy. Amano takes over the agency's helm from Mohamed ElBaradei, 67, an Egyptian-born lawyer who served in the post for 12 years and recently acted as the West's representative in negotiations with Iran to have it export the majority of its enriched uranium for processing into reactor fuel. 