VIENNA (Reuters) - The UN nuclear chief called on Monday for national safety tests on all the world's reactors within 18 months, followed by international inspections to help prevent any repeat of Japan's atomic crisis three months ago. Yukiya Amano, opening a ministerial meeting in Vienna on strengthening safety standards after the Fukushima emergency, said UN experts should be allowed to carry out random safety reviews of nuclear power plants. His proposals - aimed at ensuring that nuclear plants can withstand extreme events such as the earthquake and tsunami that crippled Fukushima - may prove controversial for states which want to keep safety an issue strictly for national authorities. "Public confidence in the safety of nuclear power has been badly shaken," Amano, director general of the International Atomic Energy (IAEA), said in a speech to ministers and regulators from the UN body's 151 member states. "However, nuclear power will remain important for many countries, so it is imperative that the most stringent safety measures are implemented everywhere." Amano, a veteran Japanese diplomat, said nuclear safety would remain a national responsibility - and that governments would have the main task of testing, if only in theory, whether reactor systems could withstand various stresses. But he also made clear he wanted the UN agency to play a greater role. "IAEA review of every one of the world's 440 operating nuclear reactors in just a few years is not a realistic proposition. I therefore propose a system based on random selection," he said. Japan's crisis has prompted a rethink of energy policy around the world, underlined by Germany's decision to shut down all its reactors by 2022 and an Italian vote to ban nuclear power for decades. At the June 20-24 meeting, IAEA member nations will begin charting a strategy on boosting global nuclear safety, but differences on how much international action is needed may hamper follow-up efforts, diplomats say. Russia wants to move toward making the UN agency's safety standards compulsory, but many other countries oppose this. Currently there are no mandatory, international nuclear safety regulations, only IAEA recommendations which national regulators are in charge of enforcing. Russia's atomic energy chief Sergei Kiriyenko welcomed Amano's proposals, telling the conference that "we are delighted that they are very much in keeping" with Moscow's views. Japanese officials have come under fire for their handling of the emergency and the authorities have admitted that lax standards and poor oversight contributed to the accident. Three reactors at the Japanese complex went into meltdown when power and cooling functions failed, causing radiation leakage and forcing the evacuation of some 80,000 people. "In the light of the Fukushima Daiichi accident, thorough and transparent national risk assessments should be made of all nuclear power plants in the world," Amano said. "They should focus on safety margins against extreme natural hazards, such as earthquakes, tsunamis and floods. This could be done within 12 to 18 months." He gave no details of how such assessments would be carried out. Typically experts speak of "stress tests" which provide for theoretical and practical simulations of how power plant systems would respond to various "stress" events, such as earthquakes. Amano said these national assessments should be followed by IAEA expert reviews to check operational safety emergency preparedness, and the effectiveness of regulatory systems. "I propose that countries with nuclear power should agree to systematic, periodic peer reviews by the IAEA," he said. "The agency could conduct an international safety review of one nuclear power plant in 10 throughout the world over, say, a three-year period."