世界各国领导正会聚伦敦参加联合国大会，此次大会议题可能会涉及叙利亚问题，虽然该问题并未正式出现在会议议程中。
Discussions are also expected to centre on Iran's nuclear programme and the video that has prompted anti-US protests across the Muslim world.
President Barack Obama is due to focus on the Middle East when he gives one of the opening speeches on Tuesday.
His address comes six weeks before the US presidential election.
But it is not to be seen as a campaign speech, according to White House spokesman Jay Carney.
"I would expect the president to address the recent unrest in the Muslim world and the broader context of the democratic transitions of the Arab World."
'Extremely bad'
Syria's 18-month conflict is not formally on the UN General Assembly's agenda but it is likely to be addressed by several speakers on the opening day, including UN Secretary General Ban Ki-moon, French President Francois Hollande and Qatari emir Sheikh Hamad bin Khalifa Al-Thani.
Mr Hollande, in his first appearance at the assembly, is also expected to call for backing for an international force to be sent to the West African state of Mali to help dislodge Islamist militants who have taken over the north of the country.
The UN Security Council has been unable to reach agreement on the Syria crisis and on Monday UN envoy Lakhdar Brahimi warned that the situation was "extremely bad and getting worse".
While he did not have a full plan, he said he had "a few ideas". Mr Brahimi has just visited Damascus as well as refugee camps in neighbouring Jordan and Turkey.
The BBC's Barbara Plett says that diplomats have played down expectations for Mr Brahimi's mission, with no sign of fundamental divisions on the council being bridged.
