The Iraqi National Assembly today bowed to international pressure and reversed last-minute voting changes which made the proposed constitution virtually undefeatable.

The Shia-led assembly accepted criticism from the United Nations and voted 119-28 in favour of changing back rules governing next week's referendum, altered three days ago to ensure the charter's passage.

Under the substitute rules, which had been approved by both Shia and Kurdish MPs, two-thirds of the electorate in three provinces had to vote "no" for the constitution to fail. In contrast, only 50 per cent support was required for ratification.

The alteration raised the bar to a level almost impossible to meet: in a province of 1 million registered voters, for example, 660,000 would have had to vote ''no'' - more than are expected to turn out in many rebel-held regions.

"The Government is completely keen to make the constitutional process legitimate and of high credibility and we are concerned about the success of this process rather than the results of the referendum," a spokesman, Laith Kubba, said.

The last-minute change enraged leaders of the Sunni minority, who are opposed to the constitution. Leaders said that the Government was moving the goalposts to push it through despite their reservations that its provisions for federalism will carve up the state along ethnic and religious lines.

Now, it has reverted to its original framework whereby a two-thirds majority of voters who actually turn out in three provinces could block the constitution, rather than the two-thirds of "registered voters" recquired under the rule change.

Sunnis, who make up only 20 per cent of the population, said that any voter who had registered but could not make it to polling stations on October 15 - a likely scenario in many areas - would effectively be counted as having voted "yes" under the rule change.

Legal experts from the United Nations had decried the changes, warning they were unlikely to meet international standards and their perceived unfairness would probably have further fuelled the insurgency.

An UN officer praised parliament for reversing the decision, saying that he believed Sunnis would now take part in the referendum. "Even if they (the Sunnis) vote no, what the Assembly did today is more democratic than what it did several days ago," the official said.

He added, however, that the parliament had added three conditions to its resolution asserting its legal right to challenge the outcome of votes in particular regions if it felt voters had been intimidated.

The original rules, now restored, mean that Sunnis can veto the constitution by getting a two-thirds ''no'' vote in three provinces, even if the charter wins majority approval nationwide. Sunni Arabs are dominant in four of the 18 provinces.

Sunnis fear that the loose federalism of the new laws will encourage the Kurds and the Shia to form largely independent oil-rich regions, while the Sunni Triangle, in the grip of an insurgency, is a desert with virtually no natural resources.

An IGC report last week said "the situation appears to be heading for . . . de facto partition and full-scale civil war. Options for salvaging the situation are gradually running out."

The vote on the constitution is a key stage in the country’s political transition is being held just four days before Saddam Hussein and seven of his former aides are due to go on trial over a massacre of Shiite villagers in 1982. They face the death penalty if convicted.

Al-Qaeda’s Iraq branch, headed by Iraq’s most wanted man Abu Musab al-Zarqawi, urged Sunnis to boycott the referendum, saying calls by Sunni groups for a "no" vote were meaningless.

"Do not participate in conferring legitimacy on the infidels," it said in an internet statement, adding that joining the vote would give "the crusaders a cover to decide your fate as they see fit.

Meanwhile, the US military said about 2,500 US soldiers launched a new operation against insurgents in the restive Al-Anbar region in the Euphrates River valley.

The new offensive, codenamed River Gate, aims "to deny Al-Qaeda in Iraq the ability to operate in the three Euphrates River Valley cities and to free the local citizens from the insurgents’ campaign of murder and intimidation."

Officials are now racing to prepare for the referendum vote, distributing five million copies of the constitution across Iraq. The UN mission has delivered more than 2 million kilograms (4.4 million pounds) of ballots, polling boxes and voter screens.

But many sources inside and outside have warned that the number of violence of insurgent attacks are certain to increase in the next ten days.

"We believe that the insurgents will try to make a surge in their attacks inside Baghdad because of its value in trying to convince the people that this government cannot protect them and also in terms of trying to make the results of the election illegitimate," Major General William Webster, who heads coalition troops in Baghdad, told reporters.

• A bomb exploded at the entrance of a Shia Muslim mosque in Hillah, south of Baghdad, today as hundreds of worshippers gathered for prayers on the first day of Ramadan and for the funeral of a man killed in an earlier bombing. At least 25 people were killed and 87 wounded.

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