UN Secretary-General Ban Ki-moon challenged world leaders on Wednesday to cleanse the globe of nuclear weapons, tackle the threat of catastrophic climate change and combat growing poverty from the global financial crisis. The UN chief warned presidents, prime ministers and diplomats from the UN's 192 member states that "no nation, large or small, can violate the human rights of its citizens with impunity." He called for greater efforts to achieve peace in Darfur and Somalia. He urged a revival of negotiations to achieve a Mideast peace with Israel and Palestine live side-by-side in peace. And he pledged to see the Afghans "through their long night" and stand as well with the people of Pakistan. "Amid many crises - food, energy, recession and pandemic flu, hitting all at once - the world looks to us for answers," Ban said in the the opening address to the General Assembly's 64th ministerial session. "If ever there were a time to act in a spirit of renewed multilateralism, a moment to create a United Nations of genuine collective action, it is now." A host of new faces were following Ban to the podium at this last General Assembly ministerial session in the UN's landmark headquarters before it closes for renovation later this fall - US President Barack Obama, Russian President Dmitry Medvedev, China's President Hu Jintao and Japan's newly elected Prime Minister Yukio Hatoyama, to name a few. Obama echoed Ban's call for global engagement, marking a sharp contrast in US policy from his predecessor, George W. Bush. "We have reached a pivotal moment," the US leader said. "The United States stands ready to begin a new chapter of international cooperation - one that recognizes the rights and responsibilities of all nations." "With confidence in our cause, and with a commitment to our values, we call on all nations to join us in building the future that our people deserve," Obama said. A day after about 100 heads of state and government, in the largest-ever summit on global warming, exchanged views on how to reach a new global accord to combat climate change, Ban again exhorted the leaders to "rise to the greatest challenge we face as a human family." "This year I have traveled from the ice rim of the Arctic to the steppes of Mongolia," Ban said. "I have seen, first-hand, the effects of climate change on our planet and its people." The UN chief also urged leaders to "make this the year we agreed to banish the bomb," to address the "red flags of warning" about a global economic recovery and make a fresh push to achieve UN anti-poverty goals, especially reducing maternal and child mortality rates which remain very high, according to his prepared text. Brazilian President Luiz Inacio Lula da Silva told the assembly that "what countries like Brazil have proven is that, at times of crisis, we must still carry out old social and development programs." "Yet I have no illusions that we might solve our problems alone within our own borders because the global economy is interdependent we are all obliged to intervene across national borders and must, therefore, re-found the world economic order," Lula said. General Assembly President Ali Treki, of Libya, echoed the need for international unity. "The international community has learned from experience that transnational threats and the multiple crises facing the world today can only be addressed through responsible international cooperation," he told the audience in the assembly chamber that included about 120 world leaders. Security around the sprawling UN complex and adjacent neighborhood was exceedingly tight because of the VIP participants, especially Obama who also spoke at Monday's climate summit and will be back here Thursday to chair a Security Council meeting on disarmament and curbing the spread of nuclear weapons. Obama was applauded warmly, but he did not receive a standing ovation. Libyan leader Moammar Gadhafi applauded at the end but Iran's President Mahmoud Ahmadinejad, who listened without an earpiece, did not. There has been praise for the new American commitment to working with countries rich and poor, large and small, to solve global problems and Obama's outreach to the Muslim world. On Tuesday - in addition to focusing on reducing US carbon emissions, a Mideast summit with the Palestinian and Israeli leaders and a meeting with China's president - Obama invited 25 African leaders and African Union Commissioner Jean Ping to lunch to discuss job creation, particularly for young people, increasing trade and investment and improving agricultural productivity. Obama stressed that the lunch was not a one-off event but the start of a dialogue between his administration and African leaders, said Michelle Gavin, special assistant to the president and senior director for African affairs. She said she was certain that Obama - whose late father was Kenyan - would make a return visit to Africa "at some point," noting that he has received many invitations. The US president will chair a high-level meeting of the UN Security Council Thursday on disarmament and efforts to halt the spread of nuclear weapons and the leaders of the four other nuclear powers on the council will also speak - Medvedev, Hu, French President Nicolas Sarkozy and British Prime Minister Gordon Brown. The council is expected to adopt a resolution calling for stepped up disarmament efforts and a more intense global campaign to reduce nuclear dangers and threats of proliferation. It doesn't name any countries but the draft resolution does refer to previous council resolutions that imposed sanctions on Iran and North Korea for their nuclear pursuits. Foreign ministers from the five permanent council nations and Germany, who have been trying to curb Iran's nuclear ambitions, will meet with the European Union's top negotiator on Wednesday to discuss prospects and expectations for lower-level talks with Iranian officials on Oct. 1. Demonstrators have announced protests against Gadhafi, who was making his first UN appearance after 40 years as ruler of the oil-rich North African nation, and Ahmadinejad. There has been much speculation on whether Obama will cross paths with Gadhafi and Ahmadinejad. They are all invited to a lunch Wednesday hosted by Ban and then there is a group photo session. Gadhafi is almost certain to meet the US leader if he attends Thursday's Security Council meeting on nuclear nonproliferation to represent Libya, which is a non-permanent council member.