"Seventy-one percent of voters in Salaheddin province voted 'no' to the Iraqi constitution," Saleh Khalil Farraj told AFP.

"These are the initial results, they are not final. They must be fine-tuned and we will announce the official figure at 5:00 pm (1400 GMT)," he said.

Eighty-eight percent of all registered voters in Salaheddin had cast ballots, the official added.

In the city of Samarra, 95 percent of voters rejected the draft charter for a post-Saddam Hussein Iraq, while three percent approved.

Results from all four Sunni-dominated provinces, Diyala, Salaheddin, Al-Anbar and Nineveh, are crucial because the constitution would be rejected if two-thirds of Iraqis vote 'no' in at least three of the country's 18 provinces.

Sunni Arabs dominated Iraq under Saddam's regime even though they comprise only around 20 percent of the population.

Sunnis fear the new constitution will concentrate power in the hands of regions dominated by majority Shiites and Kurds, depriving them of essential oil revenues.

Iraqi officials counted ballots yesterday after a historic vote on a US-backed constitution with the fate of the document in the hands of a few provinces where Sunnis may muster enough "No" votes to block it.

A massive security clampdown prevented any serious insurgent attacks on voting day, with only scattered strikes reported around the country after months of Sunni Arab militant bloodshed that has killed thousands.

Rockets woke the powerful residents of Baghdad's Green Zone government compound shortly after dawn but there was no sign of any damage from the three routine strikes, officials said.

Election officials said partial results from the vote could be available as early as Sunday, but that it would take several days for the verdict to become clear.

If the constitution passes Iraq will go to the polls again in December to elect a new, four-year parliament in a step that Washington says will mark its full emergence as a sovereign democracy and new Western ally.

A "No" vote would force the country's warring factions back to the drawing board, limiting December's election to a new interim government to redraft the charter.

Meanwhile, five US soldiers were killed in Iraq on Saturday when their vehicle was hit by an improvised bomb in the western city of Ramadi, the US military said yesterday.

The statement gave no details beyond saying the soldiers were assigned to the 2nd Marine Division.