Thousands of Marines surrounded this anti-American stronghold early today and began moving in to retake control of the city and apprehend those responsible for last week's slayings of four U.S. security contractors.
The highly anticipated action, dubbed Operation Valiant Resolve, was expected to be one of the biggest military offensives since the fall of Saddam Hussein's government a year ago.
All roads leading to this city of 300,000 were cut off and barricaded with tanks and concertina wire. Working through the cold and windy desert night, Marines set up camps for detainees and residents who might flee.
Before dawn, several Marine positions on the fringes of town were hit by mortar rounds and rocket-propelled grenade fire; one Marine was reported killed.
The Marines called in air support to take out some enemy positions and said in some cases the attackers were working in groups as large as 12.
Witnesses reported gunfire overnight and said at least four homes had been hit by U.S. aerial strikes.
At daylight, Marines in armored Humvees began distributing leaflets asking residents to stay in their homes and help identify insurgents and those responsible for last week's killings. They also took over the local radio station and used bullhorns to get the message out.
"We are going to stop the anarchy inside this city," one announcement said; another asserted that insurgents were violating the peaceful tenets of Islam.
"We're being a little more firm this time. We have to let people know that the terrorists who are harming their families and violating Islam are going against peace and brotherhood," said Capt. Michael Fehm. "We're driving a wedge between the insurgents and the good people of Fallouja."
Marines said they had no plans to conduct random door-to-door searches; they intended to work from a list of addresses where intelligence suggested suspects might be hiding and weapons might be stored.
"Everyone's in position; now we'll see it develop," Maj. Gen. James N. Mattis, commanding officer of the 1st Marine Division, said shortly after 10 a.m. today.
Members of the new Iraqi army and the Iraqi Civil Defense Corps were to play support roles in the operation, but some had to be sent home today when they reported without their uniforms or ID cards, Marines said.
It was unclear how long the operation would last. The last comparable action took place in November, when U.S. troops used helicopters, tanks and aerial bombs to root out suspected insurgent cells in Baghdad and Tikrit, destroying several buildings and homes.
The U.S. action in Fallouja comes five days after insurgents there ambushed two vehicles carrying American civilian security guards as they drove through the city. Rocket-propelled grenades were fired at the two sport utility vehicles.
Captured in gruesome television images viewed around the world, scores of angry Iraqis descended on the vehicles after the attack, pulling out the bodies of the Americans, hacking them apart with poles and shovels and dragging them through the city behind cars. Two charred corpses were hung from a bridge while a mob cheered.
Today's action by the 2,500 Camp Pendleton-based Marines was the latest attempt by U.S. forces to tame Fallouja, long a caldron of anti-American sentiment and insurgent activity 30 miles west of Baghdad in the so-called Sunni Triangle area.
Under Hussein, Fallouja was a major recruiting center for the military and security services, and heavy investments were made in the city's infrastructure and services. Standards of living rose in proportion to residents' loyalty to the regime.
In recent months, U.S. troops have fired missiles into the home of an alleged insurgent, dropped bombs around the city limits and arrested the mayor. The U.S. has also tried a softer approach, halting patrols through the city and leaving security to locals.
But Fallouja's population has remained defiant. The mayor's office has been attacked every couple of months, and the local security forces have been under almost constant siege. In February, 25 policemen were killed in Fallouja during a daytime raid in which attackers rushed a police station with guns.
The latest violence started two weeks ago, when newly arrived Marines decided to resume patrols within the city limits. A firefight ensued, killing one Marine and about 18 Iraqis. Last week's attacks on the four Americans were revenge for that bloodshed, some residents said.
"The mutilation of the Americans' bodies was in retaliation for the mass killings by the Marines in that very neighborhood a week earlier," said Hayem Mahmoud, a Fallouja schoolteacher.
Since Wednesday, at least three Marines have been killed by insurgents in the area.
For days, U.S. forces have appeared eager to get back into the city. Col. J. C. Coleman, chief of staff for the 1st Marine Expeditionary Force, said he wanted the Marines to "break the backs" of Fallouja's insurgents.
But local officials predicted that the latest U.S. action would continue the cycle of violence.
"Let the Americans know that things will be much worse than their expectation if they behave badly toward the citizens of Fallouja," said Sheik Ali Saleh, head of the Badran tribe. "They will face a strong resistance."
Residents in Fallouja have been on high alert for days. Shops closed early Saturday and Sunday, and families stockpiled food awaiting the U.S. response.
"If Americans enter the city, there will be clashes with the resistance and a lot of innocent civilians will be lost," said Hamid Saleh, 41, owner of a market.
This morning, some residents could be seen fleeing west toward Ramadi, and witnesses said the Marines were allowing some cars to leave. But no vehicles were being allowed into the city, except for those carrying food or medical supplies.
Military officials hinted that residents could avoid or soften the U.S. response by identifying the attackers and handing them over. But as of Sunday evening, local police and tribal leaders said that there had been no meetings with the Marines and that they had made no progress identifying the attackers.
Marine leaders said early today that they had plans to meet with members of the town council to enlist their support.
The flare-up comes at a particularly bad time for the U.S.-led coalition, which is attempting to show that life in Iraq is improving as it prepares to hand over authority to an interim government at the end of June.
The recent violence has raised fresh questions about whether the new Iraqi security forces are prepared to take over responsibilities from U.S.-led coalition forces.
Police in Fallouja said they were overwhelmed by Wednesday's mob.
"A group of angry construction workers participated in that unacceptable act," said Lt. Col. Ali Mishaal, the deputy police chief. "It all happened so fast we could not get there in time. We are working day and night to keep our area safe. But there is still a shortage of equipment and weapons."
In an interview Sunday, Mishaal warned that a U.S. strike would be a grave mistake. "It is only going to deepen the gap between the two sides," he said. "Violence generates violence."
Perry reported from Fallouja and Sanders from Baghdad. Special correspondent Hamid Sulaibi in Fallouja contributed to this report.