Obama urges world to stand united

US President Barack ObamaBarack Obama has acknowledged the stark challenges faced by the world, but said the US cannot succeed in tackling them alone. In his first speech to the UN General Assembly, he said global problems included nuclear proliferation, war, climate change and economic crisis. He also said he was "well aware of expectations" in his presidency. But the world shared a "common future", Mr Obama said, with all nations bearing responsibility to resolve its problems. After Mr Obama left the stage the assembly began hearing from Libyan leader Col Muammar GaddafiMuammar Gaddafi - for the first time in his 40 years in power.

ranian President Mahmoud AhmadinejadMahmoud Ahmadinejad, who has previously said he does not believe the Holocaust happened, is due to speak later on Wednesday. Israel has called for a boycott of his appearance and the Germans have said they will walk out if he repeats the claim. Relatives of victims of the 1988 Lockerbie bombing protested outside the UN headquarters as Col Gaddafi was due to arrive. The Libyan convicted of the bombing was released from a Scottish prison last month. 'New coalitions'In his maiden speech to the forum of leaders from more than 120 countries, Mr Obama acknowledged the expectations that accompanied his presidency - expectations, he said, which were "not about me".

He said that when he took offic"many around the world had come to view America with scepticism and mistrust". He said some of this was based on "misperceptions" but it was also due to "opposition to specific policies". But "we share a common future", he said, and "no longer do we have the luxury of indulging our differences". Mr Obama outlined "four pillars" which encapsulated the challenges facing the world: nuclear proliferation; peace and security; preservation of the planet; the global economy. He also said "no world order which elevates one nation above others" could succeed in tackling these problems. "We must build new coalitions that bridge old divides... All nations have rights and responsibilities - that's the bargain that makes this work," Mr Obama said. The president devoted a significant proportion of his speech to the challenges of finding a peaceful settlement in the Middle East - and called for the relaunch of "negotiations without preconditions". He said he did not underestimate the scale of that challenge, but added: "I will not waver in my pursuit of peace." On Tuesday, at the UN's climate change summit, Mr Obama acknowledged that the US had been slow to act, but promised a "new era" of promoting clean energy and reducing carbon pollution. Some countries may not take kindly to his words urging greater responsibility if it sounds too much like a lecture, particularly those who feel his commitments to tackle global warning were disappointing, says the BBC's Mark Mardell in New York. 'Best hope'UN Secretary General Ban Ki-moonBan Ki-moon opened Wednesday's proceedings by telling the assembled leaders: "Now is the time to put the 'united' back into the United Nations".

He outlined problems facing the world - including "catastrophic climate change", the proliferation of nuclear weapons, and the global economic crisis - and said the world was looking to the UN for answers. "We must act for all nations and all people. So much is possible if we work together. We are the UN, the best hope for humankind, and now is our time," Mr Ban said. The order of the speeches is based on protocol, with some flexibility. A UN spokeswoman described it as a "challenging and meticulous" task to decide the order. There is an agreed order of hierarchy - with heads of state coming before heads of government and crown princes. But exceptions are made - this time UK Prime Minister Gordon BrownGordon Brown will speak before China's head of state, President Hu JintaoHu Jintao.