WASHINGTON US President Barack Obama on Tuesday called on world leaders not simply to talk, but to act to secure or destroy vulnerable stockpiles of nuclear materials, underscoring that the prospect of nuclear terrorism had emerged as one of the greatest threats to the global security. Meanwhile, in a joint communique seen by AFP, leaders of 47 nations at the US Nuclear Summit agreed to secure loose nuclear materials around the world within four years to thwart any militant plots. Obama, addressing a plenary session of the 47-nation nuclear security conference he had convened here, told world leaders that it was time not simply to make pledges but to make real progress for the security of our people. All this, in turn, requires something else, something more fundamental, he added. It requires a new mindset - that we summon the will, as nations, as partners, to do what this moment in history demands. Seeking to lend force to his warning, Obama said that dozens of countries held nuclear materials that could be sold or stolen, and that a weapon fashioned from an apple-size piece of plutonium could kill or injure hundreds of thousands of people. Terrorist networks such as Al Qaeda have tried to acquire the material for a nuclear weapon, and if they ever succeed, they would surely use it. Were they to do so, it would be a catastrophe for the world. A day after Ukraine, Canada and Malaysia offered individual undertakings to tighten controls or reduce nuclear stocks, Obama said that the problems of the 21st century cannot be solved by nations acting in isolation - they must be solved by all of us coming together. Joint undertakings towards that end will be spelled out in a communiquT from the group to be issued at days end, and more individual commitments are expected as well. Obama also announced that there would be another nuclear security conference in two years, and that the President of South Korea, Lee Myung-bak, had agreed to be the host. That would seem to ensure a particularly close focus on the North Korean nuclear programme, just as Iran has drawn particular attention at this meeting. On Monday, Obama secured a promise from President Hu Jintao of China to join negotiations on a new package of sanctions against Iran, administration officials said, but Hu made no specific commitment to backing measures that the United States considers severe enough to force a change in direction in Irans nuclear programme. In a 90-minute conversation here, Obama sought to win more cooperation from China by directly addressing one of the main issues behind Beijings reluctance to confront Iran: its concern that Iran could retaliate by cutting off oil shipments to China, according to media reports. The Chinese import nearly 12 percent of their oil from Iran. Obama assured Hu that he was sensitive to Chinas energy needs and would work to make sure that Beijing had a steady supply of oil if Iran cut China off in retaliation for joining in severe sanctions. American officials portrayed the Chinese response as the most encouraging sign yet that Beijing would support an international effort to ratchet up the pressure on Iran and as a sign of international unity on stopping Irans nuclear programme before the country can develop a working nuclear weapon. Agencies add: Leaders of 47 nations at a Washington summit agreed Tuesday to secure loose nuclear materials around the world within four years to thwart any militant plots, in a joint communique seen by AFP. The pledge met the challenge laid down to the Nuclear Security Summit by host US President Barack Obama, who warned that catastrophe looms if extremist groups ever manage to build a nuclear bomb. The draft promised greater efforts to block non-state actors from obtaining the building blocks for nuclear weapons for malicious purposes. We welcome and join President Obamas call to secure all vulnerable nuclear material in four years, as we work together to enhance nuclear security, the leaders said in the joint communique to be released shortly and seen by AFP. They outlined measures to combat nuclear trafficking, including sharing information and expertise in detection, forensics and law enforcement. The leaders said they recognise the need for cooperation among states to effectively prevent and respond to incidents of illicit nuclear trafficking. The leaders also underlined that the main structure for combating nuclear proliferation remains the UN watchdog, the International Atomic Energy Agency, which they said has the essential role. The summit participants vowed to ensure that it continues to have the appropriate structure, resources and expertise. The summit communique, a copy of which was obtained by Reuters, called for new controls on plutonium and highly enriched uranium and separated plutonium, key components of nuclear weapons, and a crackdown on nuclear smuggling. But, in a nod to some developing countries seeking to launch civilian nuclear programmes, the summit agreed that increased security steps will not infringe upon the rights of states to develop and utilise nuclear energy for peaceful purposes. The summit encouraged nations to covert nuclear reactors from highly enriched uranium fuel to less risky low enriched fuel. The countries also recognized the continuing role of the nuclear industry, including the private sector, in security work and pledged to cooperate with the industry to improve the overall nuclear security culture. The nations will leave the first nuclear security summit Tuesday with a step-by-step instruction manual on how to keep nuclear stockpiles and fissile materials out of the hands of extremists. A work plan issued after the two-day summit in Washington listed steps nations should take to secure stocks of separated plutonium and weapons grade uranium and advises states on how to dispose of the dangerous materials. Participating states will consider, where appropriate, the consolidation of national sites where nuclear material is held, the document, obtained by AFP said. The plan commits the states to exercise particular care in transporting nuclear materials safely, and to account for all separated plutonium, mindful that it can be used in a nuclear device. Participating states, where appropriate, will consider on a national basis the safe, secure and timely removal and disposition of nuclear materials from facilities no longer using them, the document said. The document also advises states to convert reactors which are fuelled by high-enriched uranium, which can be used to build weapons, into facilities using low enriched uranium. While the document spells out a long list of steps nations should take, it is couched in diplomatic language which does not compel signatory nations to take such actions. Mindful of the cost and technical difficulty of securing nuclear fissile material around the world, the document also calls on nations to provide assistance to other nations that need it, to secure or export stockpiles. No financial specific dollar figure was mentioned, and no specific mechanism for providing financial support was laid out.