The United Nations has attacked rule changes by the Shia-led Government in Iraq that make it harder for voters to reject the draft constitution in next week’s referendum.

The change, which has angered Sunni leaders who oppose the document, was "not acceptable and would not meet international standards", said Jose Aranaz, a legal adviser to the UN legal team in Iraq.

Parliament approved new rules on Sunday which require a simple majority of those turning out to vote to approve the draft constitution, while it would take two-thirds of registered voters in at least three provinces to reject it.

"We have expressed our position to the national assembly and to the leadership of the Government and told them that the decision that was taken was not acceptable and would not meet international standards," said Mr Aranaz.

A number of Sunni Muslims have already called for a "no" vote to the constitution because they believe that its federalist provisions will divide the country. Sunnis form a majority in three provinces in Iraq, but they largely boycotted general elections earlier this year.

"You cannot have two different meanings in one article. It’s using interpretation to your own benefit," according to the UN official who requested anonymity.

According to Article 61C of the Transitional Administrative Law, a two-thirds vote in each of any three provinces is enough to reject the draft constitution in the October 15 referendum.

The original article reads: "The general referendum will be successful and the draft constitution ratified if a majority of the voters in Iraq approve and if two-thirds of the voters in three or more governorates do not reject it."

On Sunday, parliament changed the rules to read "voter" in the first instance and "registered voter" in the second, making it more difficult for those opposed to the draft constitution to reject it.

Times Recommends

• Zardari still has to tackle tough questions
• Material evidence 'debunks' Turin Shroud
• BBC criticised over Uganda gay execution poll