The outcome of Saturday's referendum on Iraq's new constitution is shrouded in uncertainty, reports Salah Hemeid Against a background of suicide car bombs, roadside explosives and drive-by shootings, Iraqi leaders are making a last ditch attempt to reach agreement over the draft constitution, widely seen as the make or break point in war-torn Iraq's tortuous political process. The attacks came as Shia and Kurdish leaders continued to negotiate with Sunni Arabs in an attempt to win Sunni support for the controversial document ahead of Saturday's referendum. Jalal Talabani, the Kurdish leader and provisional president -- aided by US ambassador Zalmay Khalilzad -- led attempts to persuade Sunnis to accept several amendments to the charter. Yet with only two days left before the referendum there is little time to resolve differences between the two sides over key issues which include the federalism Shia and Kurds insist on, and the role of former Baathists in the country's political process. Hajim Al-Hassani, speaker of the provisional parliament, announced late Tuesday an agreement had been reached under which the constitution would be revised by the next parliament, due to be elected in December. The move was an attempt to convince Sunnis to endorse the constitution and encourage them to vote in the referendum. The Iraqi Islamic Party, one of Iraq's main Sunni Arab political groups, immediately accepted the compromise deal and said it will urge supporters to back the new constitution. Other Sunni groups, including the Association of Muslim Clerics and the Iraqi National Dialogue, were less amenable. Muthana Harith Al-Dhari, spokesman for the clerics association, dismissed the changes as cosmetic. "This constitution will sow the seeds of division and should be rejected," he told Al-Arabiya television. Saleh Al-Mutlaq, spokesman for the Iraqi National Dialogue, urged the Islamic Party, the Iraqi branch of the Muslim Brotherhood, to reject the deal. While both groups have said they will leave it up to voters to decide whether to boycott the referendum they are urging those who do decide to vote to reject the constitution. Sunni Arabs fear the document, drafted by a Kurdish-Shia dominated parliament, undermines Iraq's Arab identity and will create two oil-rich and nearly autonomous regions -- a Kurdish one in the north and a Shia one in the south -- leaving them stranded in the middle. Under rules set by Iraq's American-appointed administration the constitution can be voted down by a simple majority, or if two-thirds of voters in three out of Iraq's 18 provinces say "no". Sunnis comprise the majority in four provinces. A "no" vote is likely to heighten tensions, and will be presented by insurgents -- who have demanded a boycott -- as a moral victory. Most members of the majority Shia, and of the Kurdish community, support the draft. The overwhelming victors in January's elections, they have defended provisions rejected by the Sunnis during the protracted talks over what the new constitution should contain. Shia and Kurdish leaders are calling on their supporters to turn out in force to endorse the constitution in an attempt to boost turn out and counter Sunni mobilisation. With Washington seeking to lay the groundwork for an eventual exit strategy, US officials are eager to see the passage of the constitution, fully aware that rejection will hamper the plans to start pulling out some troops next year. During the protracted negotiations US Ambassador Khalilzad played a central role and reportedly made several proposals in a bid to bridge the gulf between the two sides. US President George W Bush, who has mounted a major diplomatic push to get the constitution passed, including dispatching American envoys to major Middle East capitals, said he was confident Iraqis would make their voices heard above the bloodshed. "I expect violence because there's a group of terrorists and killers who want to try to stop the advance of democracy in Iraq," Bush said in an interview with NBC's Today show. "I also expect people to vote, which is a remarkable achievement." Just how high the stakes are in Saturday's referendum was clearly on the minds of President Hosni Mubarak, King Abdullah II of Jordan and King Hamad Al Khalifa of Bahrain when they met on Monday in Cairo. "The leaders have agreed on the necessity of supporting the Iraqi people at this crucial stage, including the referendum on the constitution and means to bring the political process to fruition," said Egypt's presidential spokesman Sulaiman Awad following the mini summit. Yet even if the constitution is accepted US and Iraqi officials are under no illusions that it will bring any immediate improvement in the security situation. Iraq's Interior Minister Bayan Jabr told the London-based Asharq Al-Awsat newspaper that it will take at least five years to put down the insurgency while General George Casey, America's senior commander in Iraq, said it was "entirely possible" the situation would worsen if the text were approved over a large Sunni no vote. Meanwhile, Arab League Secretary-General Amr Moussa dispatched a team to Baghdad in an attempt by the pan-Arab organisation to help resolve Iraq's political stalemate. Undeterred by an attack on the delegation in Baghdad, Moussa, who has warned that Iraq is on the brink of civil war, plans to visit Baghdad personally before the end of the month to lay the groundwork for an Iraqi "reconciliation conference". But with the political process in Iraq tied in so many political knots and no sign of a halt in the insurgency it remains to be seen whether a yes vote in the referendum will open a window of opportunity in the war-torn country.