UNITED NATIONS  - War in Syria, mounting tensions over Iran’s nuclear drive and anti-Western protests across the Muslim world will cast a shadow over the annual UN gathering of world leaders starting Tuesday.Words of warning and defiance are expected when US President Barack Obama, Iran’s leader Mahmoud Ahmadinejad and Israel’s Prime Minister Benjamin Netanyahu join more than 120 heads of state and government at the UN General Assembly.Because of international divisions over the 18-month-old Syria conflict, the UN is holding no formal meeting on the civil war.But Obama and Western leaders are expected to call for action in their speeches. The US president is one of the first speakers on Tuesday after the event is opened by UN Secretary-General Ban Ki-moon.“We’re going to have to work to prevent Iran from getting a nuclear weapon,” Obama said previewing his speech Saturday. “We’re going to have to make sure that not only our diplomatic posts are safe, but we go after folks who threaten or try to kill Americans.”Obama will hope to win a few domestic political points by cutting a statesman like figure with his annual speech to the United Nations, and will offer his most detailed explanation yet of the US response to the rash of anti-American protests in the Arab world.While in New York, he will also repay former president Bill Clinton for his acclaimed speech lauding the Obama presidency at the Democratic National Convention, by appearing at the annual Clinton Global Initiative meetings.Syria will also dominate a Security Council ministerial debate on links with the Arab League on Wednesday, the European Union is set to launch a new appeal for humanitarian funds and a Friends of Syria ministerial meeting is planned for Friday.Diplomatic wounds over Syria are not close to healing. Neither Russia nor China, which have three times vetoed Security Council resolutions on Syria, will be represented by a senior leader in New York. Assad is expected to send his foreign minister.Ahmadinejad is in New York for probably his last appearance at the General Assembly. This time there is feverish speculation that Israel is planning a military strike on bunkered Iranian nuclear facilities that Tehran insists are for peaceful purposes, but Western nations say hide attempts to develop a nuclear bomb.Ahmadinejad speaks to the assembly on Wednesday, when a new walkout is predicted if the Iranian leader repeats one of his toxic remarks about Israel.Top officials from Britain, China, France, Germany, Russia and the United States - which are attempting to negotiate with Iran - are to meet on Thursday just after Israel’s prime minister addresses the assembly.Netanyahu and Obama will not meet in New York and this has heightened speculation of a rift between the two. The United States and its allies have stepped up warnings to Iran, however, that time is running out for a negotiated solution to the showdown. Netanyahu will take the UN stage two slots after Palestinian president Mahmud Abbas. Last year, Abbas took center stage with his emotional bid for full membership of the UN, which was thwarted by the United States.OIC Secretary General Ekmeleddin Ihsanoglu told AFP that world leaders must “come together in solidarity and as a political gesture and show of goodwill” to condemn the film and “to underline the ethical responsibility of all to respect human dignity and not to insult the ‘other’ over most sacred values.”He said leaders must break “the vicious circle of provocation and violent reaction instigated by the marginal extremist forces of the societies on both sides of the so-called divide.”The week-long debate for world leaders will also see key meetings on the conflicts in Mali, Democratic Republic of Congo, Somalia and Yemen.