Some 2,500 U.S. troops along with Iraqi forces launched their second major offensive in western Iraq in a week, sweeping into three towns to take them back from insurgents who drove out Iraqi forces and killed Marines there last month.
The U.S. military announced its first casualties of the offensives, with four servicemembers killed by roadside bombs during the fighting and a fifth elsewhere.
The assaults in western Iraq aim to put down al-Qaida in Iraq and other Sunni-led insurgent groups that have waged a campaign of violence aimed at wrecking a crucial Oct. 15 national vote on a new constitution. The United States has hoped the new charter would bring together the country's fractious commmunities, but Sunnis sharply oppose it.
Sunni Arab moderates threatened Tuesday to boycott the voting after the Shiite-led parliament passed new rules over the weekend that make it effectively impossible for Sunnis to defeat the charter at the ballot box.
The new rules deepened alienation over the political process among Sunnis.
"Boycotting the referendum is a possible option ... because we believe that participating in the voting might be a useless act," said Saleh al-Mutlaq, a leading Sunni politician.
Meanwhile in Baghdad, a suicide attacker set off a car bomb at the main entrance to the heavily fortified Green Zone, a district of Iraqi government buildings and the U.S. and British Embassies. The powerful blast killed two policemen.
The attack came on the first day of Ramadan, the holy Islamic month of fasting.
The military launched its latest offensive in a cluster of cities in the Euphrates River valley about 140 miles northwest of Baghdad. Code-named River Gate, it was the largest U.S. offensive in the troubled Anbar region of western Iraq this year. It also included hundreds of Iraqi troops, the largest Iraq contingent of any of the offensives this year.
Air strikes by U.S. warplanes and dozens of helicopters set off explosions that lit up Haqlaniyah, Parwana and Haditha before dawn Tuesday.
Some of the strikes took out bridges across the Euphrates in the area to prevent militants from escaping over them into the desert.
The military launched a similar offensive on Saturday, 93 miles upriver, by the Syrian border. That "Iron Fist" operation, which continued Tuesday, concentrated in the towns of Sadah, Karabilah and Rumana, aiming to uproot al-Qaida in Iraq insurgents who receive reinforcements and supplies from inside Syria. At least 57 insurgents have been killed in that operation.
The newest operation is "step forward to eliminating insurgents and giving the country back to the Iraqi people," said said Col. Stephen W. Davis, who underlind that it would help people in the Haditha area freely vote in the upcoming referendum on the country's draft constitution, the AP reports.