And, in what was seen as another blow to the United States and Britain, the secretary general of the Arab League warned that adopting the constitution in its current form will be a " true recipe for chaos" with reverberations around the region.
The draft document, approved by the Shia and Kurdish factions but rejected by Sunni Arabs, was finally delivered to the National Assembly at the weekend.
But Amr Moussa, the Arab League secretary general, said yesterday: "I share the concerns of many Iraqis about the lack of consensus on the constitution. I do not believe in this division between Shia and Sunni and Muslims and Christians and Arabs and Kurds.
"I find this is a true recipe for chaos and perhaps a catastrophe in Iraq and around it."
Mr Moussa, a former Egyptian foreign minister, said there was also concern in the Arab world that the draft text denied Iraq's "Arab identity". The text states that Iraq is "part of the Islamic world and its Arab people are part of the Arab nation". President George Bush had welcomed the draft constitution and said the referendum was a chance for the country to " set the foundation for a permanent Iraqi government". He said that the document "contains far-reaching protections for fundamental human freedoms including religion, assembly, conscience and expression".
But Mr Bush added: "We can expect ... atrocities to increase in the coming months because the enemy knows its greatest defeat lies in the expression of free people in freely enacted laws and at the ballot box."
The ratification of the constitution at the referendum, and the subsequent elections, remain a key plank of the US-British exit strategy from Iraq and a rejection will mean the political process will have to start again from scratch.
The Sunnis - who object to the federal structure inherent in the draft, claiming it will leave the Shias and the Kurds in control of the oil-producing areas - have begun a voter-registration drive. Three out of Iraq's 18 provinces have to vote "no" by a majority of two-thirds in the referendum for the constitution to be rejected. Sunni leaders yesterday maintained this was eminently possible with large Sunni populations in four provinces.
The "no" campaign has also been bolstered by the support of the radical Shia cleric Muqtada Sadr, who commands the heavily armed Mehdi Army militia.
Hussein al-Falluji, a senior Sunni negotiator, said: "We cannot agree to the constitution. We have objections which are the same as we have had from day one. If there is no forging of the results. I believe the people will say 'no' to the American constitution."
President Jalal Talabani, Iraq's President, a Kurd, appeared to concede that a rejection at the referendum may well take place. "If they [Sunni voters] do participate, then the constitution will probably fail and new elections will have to take place to create a new drafting committee to come up with a new constitution," he said.
One Sunni political grouping, the Iraqi Islamist Party, yesterday said there was still room for negotiations. "We might say yes to the constitution if the disputed points are resolved."
Shia officials are adamant that they had already offered all concession possible to the Sunnis. In one of the main Sunni protest marches, in Tikrit, Saddam Hussein's home town, demonstrators carried pictures of the imprisoned deposed dictator as well as Muqtada Sadr and chanted slogans against the "Zionist, American, Iranian constitution".
Violence continued across the country with insurgent rocket attacks on Iraqi government and US troops. Iraqi police said they had discovered 13 bodies in three Western towns.Reuse content