Sunni leaders responded angrily, some of them saying they suspected fraud and accusing American officials and the Shiite parties that dominate the government.

Saleh Al-Mutlak, an Iraqi Sunni politician who represents the National Dialogue movement, said he estimated most Sunni Arabs voted "No" despite a US-brokered deal with one Sunni political party.

He questioned the validity of any result.

"[US Secretary of State] Condoleezza Rice made a statement," he told reporters.

Speaking in London as votes were still being counted in Iraq, Rice said the charter had "probably passed".

"I believe it is a signal to the Electoral Commission to pass the constitution," Al-Mutlak said.

The same position was echoed by Sheik Abdul-Salam Al-Kubaisi, a prominent scholar with the influential Association of Muslim Scholars, the highest Sunni religious authority in Iraq.

"There is no doubt that America has interfered in the process, since they and the Shiite government are supervising the whole operation, and since both want this draft to pass," he was quoted as saying by the AP.

US military helicopters, Humvees and armored vehicles were helping transport the ballot boxes from polling stations to counting centers in the provincial capitals.

Residents said US aircraft bombed some areas in the city of Ramadi, west of Baghdad, that strongly opposed the constitution, reported Reuters.

A doctor said 25 people had been killed.

The US army said it killed at least 50 "insurgents" by F-18 and helicopter strikes on a suspected safe house in Abu Faraj region, north of Ramadi, while 20 more were killed to the east of the city as they tried to lay a roadside bomb.

Carina Perelli, who leads a team of UN advisers working with Iraq officials, stressed that final results were still days away and any early estimates were "impressionistic."

The final tallying was likely to begin on Monday and to last into Tuesday.

If the constitution passes, Iraqis will vote again in December for a new, four-year parliament.

Iraq's President Jalal Talabani announced that elections, whether they be for a four-year parliament or a new interim assembly, would be held on December 15, the last possible day to hold them according to the rules of the interim constitution.