Iraqi politicians on Tuesday insisted a draft constitution largely crafted by Shia and Kurds would be put to a parliamentary vote this week, in spite of strong opposition from Sunni Arabs.

The approval of the text, however, would set the stage for a referendum battle, in which the minority Sunni Arabs will campaign to block a document they say could fragment the country.

The dissent by Sunni leaders also marks a setback for the declared policy of the US, which had lobbied hard to give the Arab minority influence in the debate over the constitution as a way of undercutting support for the insurgency.

Minutes before a midnight deadline for presenting the constitution on Monday Hachem al-Hassani, parliamentary speaker, announced that the national assembly had received a draft but that it would take a further three days of consultations so that “the constitution pleases everyone”. He then adjourned parliament without either reading the constitution or calling a vote.

The document appeared in the Iraqi press on Tuesday, and Shia, Kurdish and Sunni politicians said significant changes to the text were unlikely, as was Sunni Arab agreement to the draft.

“I don't think there is any chance to convince the Sunnis and I don't think that the Shia will accept any changes,” said Mahmoud Othman, an independent Kurdish parliamentarian.

How much pressure the US is willing or able to exert at this point is unclear. Zalmay Khalilzad, US ambassador, has been closely involved in the talks, and some Iraqi politicians have detected a recent shift from bringing the Sunni on board in an attempt to weaken the insurgency, to producing a draft quickly for domestic political purposes.

In accord with the demands of the Shia Islamist-dominated majority bloc, the document declared that Islam would be “a fundamental source of legislation” and that no law should contradict “the principles of Islam's jurisprudence”.

This language, however, is less explicit on the role of Islam in governance than many had expected.

The draft also contains language that would allow the creation of regional governments with wide-ranging powers. The Sunni say they accept the Kurdish self-rule zone as a fait accompli but that the principle would splinter Iraq if it was extended. “If they implement the regions, I think there will be civil war in Iraq. There will be two Islamic regions in Iraq: one in the south, supported by Iran, and one in the middle and the west, supported by extremist Islamists, Sunnis,” said Saleh al-Mutlek, the most vocal of the Sunni representatives.

Shia from the impoverished but oil-rich southern provinces have long pushed for their own federal region. In the last two weeks the leadership of the Supreme Council for Islamic Revolution in Iraq, the most powerful of Iraq's Shia political parties, has also strongly backed the principle.

Mr Mutlek called the adoption of the draft document illegal, saying it violated earlier assurances made to the Sunni that a draft would be approved by consensus. He said he would now campaign to block the constitution in a referendum in October. While Washington has emphasised the political progress in Iraq, the US military is struggling to defeat the insurgency.

Donald Rumsfeld, defence secretary, on Tuesday said completing the constitution would be unlikely to end the violence in Iraq. But he played down concerns about a civil war.

“There's been a concern about the possibility of a civil war since before the war [in Iraq] started. It hasn't happened. Indeed, quite the contrary has taken place.”

Additional reporting by Dhiya Rasan and Demetri Sevastopulo in Washington

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