The UN General Assembly opened its 64th session on Tuesday at the UN Headquarters in New York, as world leaders are set to gather here in the next few days for a string of summits on pressing global challenges.

In a world still shrouded by a financial and economic crisis rarely seen in decades, and hassled by environmental degradation and regional conflicts, hot topics will include climate change, nuclear disarmament, development, global financial and economic governance as well as international peace and security.

About 130 heads of state or government are expected to take the podium at the assembly hall and some will also stay for other eye- catching events, including a climate summit and a Security Council summit on nuclear disarmament.

Climate change

Climate change is set to be one of the dominant issues at the General Assembly. The climate summit, to be convened by UN Secretary-general Ban Ki-moon on Sept. 22, will be an opportunity to boost cooperation between developing and developed countries before a historic UN climate conference in December in Copenhagen.

In a move that signals a change in US climate policy from its past, US President Barack Obama will address the opening session of the one-day event, on which the UN chief has pinned hopes that it will help mobilize the "political will and vision needed" to clinch a deal on greenhouse gas emissions at the Copenhagen talks.

In keeping with UN tradition, the US president will also address the General Assembly on the first day of its annual debate, on Sept. 23, at which all the leaders from the UN's 192 member states will make statements.

Nuclear disarment

On Sept. 24, or the second day of the general debate, a summit- level Security Council meeting on nuclear non-proliferation will be held under the chairmanship of Obama, whose country holds the 15-member body's rotating presidency in the month.

It marks the first time that a US president leads a Security Council meeting. "This session will focus on nuclear non-proliferation and nuclear disarmament broadly, and not on any particular countries. Key areas to be highlighted will include arms control and nuclear disarmament, and strengthening the NPT ( Nuclear Non-Proliferation Treaty) regime, and denying and disrupting trafficking in and the securing of nuclear materials," US Ambassador to the UN Susan Rice said.

To this end, the United States has drafted a Security Council resolution calling on all nuclear powers to work toward "general and complete disarmament under strict and effective international control."

The US draft was hailed by analysts as another sign of policy shift taken by the Obama administration, a far cry from the previous Bush administration, which had ignored disarmament commitments made by previous US governments.