World leaders are gathering in New York for a UN General Assembly likely to be dominated by Syria, although it is not formally on the agenda, BBC News reports.

Discussions are also expected to centre on Iran's nuclear program and the video that has prompted anti-U.S. protests across the Muslim world.

U.S. President Barack Obama is due to focus on the Middle East when he gives one of the opening speeches on Tuesday, Sept 25.

His address comes six weeks before the 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."

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.