Democratic uprisings across the Arab world and the Palestinians' bid for UN membership sparked excitement and hope at last year's meeting of world leaders. But with war raging in Syria and the Palestinian application sidelined, the mood as this year's UN gathering begins is one of disappointment and frustration.

More than 120 presidents, prime ministers and monarchs meeting this week under heavy security at the UN General Assembly and in sideline events will also be preoccupied by rising tension over Iran's nuclear program and the possibility of an Israeli strike against Tehran's nuclear facilities, al-Qaeda's inroads in the Sahel region of West Africa, especially in Mali, and the first decline in years in international aid to help developing countries combat poverty.

Secretary General Ban Ki-moon predicted that the ministerial session, which starts Tuesday, will be among the busiest ever, reflecting "the tumultuous time in which we live — a time of turmoil and transition." It is also taking place "against a backdrop of widespread violence linked to intolerance," he said.

Obama to address UN

Ahead of the opening ministerial session, which U.S. President Barack Obama will address, the UN chief has invited leaders to the first high-level meeting on the rule of law on Monday, hoping they "will send a strong signal to the world's people that they are serious about establishing well-functioning institutions and delivering justice."

Iran's President Mahmoud Ahmadinejad flashes the peace sign during the high-level meeting of the General Assembly on the rule of law at the UN headquarters in New York, Sept. 24, 2012. (Eduardo Munoz/Reuters )

Diplomats aren't expecting any breakthroughs on the deadlock over Syria, which Ban said "will be foremost in our minds," despite a number of sideline meetings starting Monday when the new UN-Arab League envoy Lakhdar Brahimi briefs the UN Security Council behind closed doors on his recent talks with Syrian President Bashar al-Assad and other leaders in the region.

'To increase pressure and to increase the isolation of the regime of Assad is one of the goals of this week.'—Germany's Foreign Minister Guido Westerwelle

"To increase pressure and to increase the isolation of the regime of Assad is one of the goals of this week," Germany's Foreign Minister Guido Westerwelle told reporters Sunday.

The Syrian conflict has bitterly divided the most powerful members of the Security Council, paralyzing the only UN body that can impose global sanctions and authorize military action. Russia, Syria's key protector, and China, have vetoed three Western-backed resolutions aimed at pressuring Assad to stop the violence and start political talks with opponents of his family's 40-year dictatorship who began demonstrating against his regime 18 months ago.

Germany's UN Ambassador Peter Wittig, the current Security Council president, said "change in the Arab world" will be uppermost in the minds of the leaders — as was the case at last year's session.

Egypt's President Mohammed Morsi, an Islamist who was sworn in on June 30 after the first democratic elections in the country's modern history, will be addressing the 193-member assembly for the first time on Wednesday. So too will Yemen's President Abed Rabbo Mansour Hadi, who took office in February following more than a year of political turmoil and is now trying to steer the country's transition to democracy.

Last year, Palestinian leader Mahmoud Abbas stole the spotlight with his submission of an application for Palestine to become the 194th member state of the United Nations. The United States, Israel's closest ally, made clear that it would veto any application until the Palestinians and Israelis negotiate an end to their decades-long conflict.

Abbas expected with modest proposal

Abbas is expected to come to the General Assembly on Thursday with a more modest proposal — to upgrade the Palestinian Authority's current status as a UN observer to a non-member observer state — but likely putting off the date for submission of a resolution to the assembly, where there are no vetoes, until after the U.S. presidential election in November.

The Palestinians expect overwhelming support from the assembly for the enhanced UN status, which they hope will give broad international legitimacy to the pre-1967 lines as the Palestinian border and grant them access to UN agencies and possibly the International Criminal Court.

With no sign of an end to the Security Council's paralysis over Syria, Wittig said Germany chose to focus the council's ministerial session Wednesday on something new and positive in the Mideast — "the emergence of the Arab League as a regional actor that has proved to be essential for conflict resolution."

The 21-member Arab League has shaken off decades of near total submission to the will of the region's leaders and is seeking to transform itself following the seismic changes brought about by the Arab Spring. The league has supported the rebels who ousted Libyan leader Moammar Gadhafi and suspended Syria in response to Assad's brutal crackdown against his opponents.

Iran's nuclear program on the agenda

Another issue looming large over the ministerial session is Iran's nuclear program, with Israeli Prime Minister Benjamin Netanyahu convinced that the Iranians are close to developing a nuclear weapon — which Tehran vehemently denies.

Iranian President Mahmoud Ahmadinejad, who will step down next year, makes his final speech to the General Assembly on Wednesday. Netanyahu speaks on Thursday, before a closed-door meeting of senior diplomats, and possibly ministers, from the six countries trying to rein in Iran's nuclear ambitions — the U.S., Russia, China, Britain, France and Germany.

Secretary General Ban met Ahmadinejad on Sunday and "urged Iran to take the measures necessary to build international confidence in the exclusively peaceful nature of its nuclear program," UN spokesman Martin Nesirky said.

The UN chief also raised the potentially harmful consequences of inflammatory rhetoric "from various countries in the Middle East" and "the grave regional implications of the worsening situation in Syria and underlined the devastating humanitarian impact," Nesirky said.

There will also be sessions to promote the achievement of UN anti-poverty goals by 2015, sustainable energy and an end to polio.