President Obama Tells U.N. World Can't 'Wait for America' to Lead

President Obama also told world leaders Wednesday he believes there are four pillars necessary to ensure a peaceful future: nuclear disarmament, the promotion of peace and security, preservation of the planet and a global economy that offers opportunity for all people. He said those pillars must be "the guiding principle of international cooperation."

Hear President Obama's full speech:

The time has also come to re-launch negotiations toward the long-elusive goal of Mideast peace, President Barack Obama said, adding it was time for talks without preconditions to resolve disagreements on security for Israelis and Palestinians, borders, refugees and the status of Jerusalem itself.

President Obama also restated his position that both Tehran and Pyongyang must back off their interest in nuclear arms. He said Wednesday "the world must stand together to demonstrate that international law is not an empty promise and that treaties will be enforced."

President Obama has already pressed for international efforts, telling a U.N. conference Tuesday that both rich nations and emerging economies must "do what we can when we can" to promote economic growth without damaging the planet. On Wednesday, he expanded his call for nations to work with the United States on other crises facing the world.

"Those who used to chastise America for acting alone in the world cannot now stand by and wait for America to solve the world's problems alone," President Obama said Wednesday, a day after he spoke at the U.N.'s climate change summit. "We have sought in word and deed a new era of engagement with the world. Now is the time for all of us to take our share of responsibility."

President Obama's speech is the centerpiece of a day in which he was also holding pivotal meetings with the new Japanese prime minister, Yukio Hatoyama, and Russian President Dmitry Medvedev. More than 120 presidents, prime ministers and monarchs are attending this year's 64th session of the world body.

The assembly will also hear from Libyan leader Moammar Qaddafi for the first time plus Zimbabwean President Robert Mugabe and Iranian president Mahmoud Ahmadinejad, who last week repeated his denials that the Holocaust happened.

Israel has called for a boycott of Ahmadinejad's appearance and the Germans have said they will walk out if he repeats the claim.

Also scheduled to make speeches this week are Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas, who have both rebuffed President Obama's efforts to reinvigorate stalled Middle East peace talks. President Obama held talks and a photo opportunity with the two leaders on Tuesday, but there were no concrete signs of progress.

"Extremists sowing terror in pockets of the world," President Obama said. "Protracted conflicts that grind on and on. Genocide and mass atrocities. More and more nations with nuclear weapons. Melting ice caps and ravaged populations. Persistent poverty and pandemic disease.... I say this not to sow fear, but to state a fact: The magnitude of our challenges has yet to be met by the measure of our action."

After this morning's speech, President Obama will participate in a wreath laying at the U.N. for staff members killed in the line of duty and then attend a lunch hosted by Secretary General Ban Ki Moon. This evening, the president and first lady Michelle Obama will host a reception for world leaders at the Metropolitan Museum of Art.

President Obama's U.N. address comes amid a busy week on the world stage. On Thursday, he moves on to Pittsburgh to talk with fellow world leaders about the global recession and financial regulatory reform at the G-20 economic summit.

---- Compiled from wire reports and other media sources