Skirmishes broke out between U.S. Marines and Iraqi gunmen Monday as the Marines launched Operation Vigilant Resolve (search) in the volatile city in which four American civilians were slain last week in one of the more grisly displays of violence since the war began last year.
Explosions and gunfire were heard from the city — including a string of up to 30 blasts, apparently shelling, late Monday — as Marines met resistance while probing the outer neighborhoods of the city with reconnaissance missions.
At least one Iraqi gunman was killed in the exchanges. A U.S. Marine was killed in the area earlier Monday.
Meanwhile, an Iraqi judge issued an arrest warrant for a radical Shiite Muslim cleric, Muqtada al-Sadr (search), for the slaying of another Shiite leader shortly after the Iraq war began. Al-Sadr has called for revolt against coalition forces.
Pentagon officials also promised a strong response to this weekend's violence in the Shiite suburb of Sadr City (search) in Baghdad and in the city of Najaf (search), where eight Americans and one Salvadoran were killed.
Outside Fallujah, troops dug trenches on the city's edges, sealed off roads in and out and imposed a nighttime curfew.
But insurgents in the city appeared to be gearing up for a fight. U.S. troops on the edge of the city came under fire from a mosque, said Marine Capt. Michael Fehn. The Marines and helicopter gunships returned fire.
Marines also fired on a car carrying six men with grenades and rifles, killing one and wounding two.
A witness reported that a U.S. helicopter struck a residential area in the city early Monday, killing five people. The bombing damaged five houses, said the witness, Mohammed Shawkat. There was no immediate U.S. comment on the report.
Two Iraqi drivers working for The Associated Press were stopped by insurgents blockading a road about six miles east of Fallujah on Monday. The rebels, armed with automatic weapons and rocket-propelled grenade launchers, searched the two vehicles before letting them go.
"In Fallujah, we're looking at small groups of disenfranchised former Baathists and regime elements who have little hope for the future," a senior U.S. Central Command official said. "That situation is not nearly as troublesome as the Shiite demonstrations that have occurred," in the other cities.
The Centcom commander said the Baghdad and Najaf violence will not go unchallenged. But, he stressed, the urgings of al-Sadr and the actions of his 3,000-member militia do not in "any way" make for a Shiite uprising.
"This is an outlaw group with its own militia that is not particularly [politically] powerful," he said, saying that violence is viewed as a "power grab" prior to the June 30 transition to Iraqi self-governance.
"We need to go after the militia forces, de-arm them and take them apart," he said. "The Iraqis are going to have to help us take care of the situation … this is not the beginning of a civil war in our view. The moderate Shiites don't want this to happen ... they want democracy."
President Bush vowed Monday that despite the increased violence against coalition forces, the June 30 deadline stands.
"We're being challenged in Iraq because there are people who hate freedom," Bush told reporters in Charlotte, N.C. "The closer we come to the deadline, the more likely people will challenge our will … I think throughout this period, there's going to be tests ... they think that we're not sincere about staying the course.
L. Paul Bremer, the top U.S. official in Iraq, cancelled a trip to Washington this week, a Senate aide said Monday. The aide said Bremer was to have given a closed-door briefing Thursday to the full Senate on the situation in Iraq, but Senate officials were informed Monday morning that the visit to Washington had been put off. No reason was given for the postponement, the aide said.
'We Want to Get the Guys'
About 1,200 Marines, joined by two battalions of the Iraqi Civil Defense Corp., surrounded Fallujah (search) with checkpoints Monday.
"The more we put our U.S. face on things out there we don't like, the more we're going to be victims of their retribution," said retired Marine Lt. Col Bill Cowan, a Fox News military analyst. "We need to put on an Iraqi face … whether they like it or not, we've got to do it."
A military spokesman said the operation would move steadily, perhaps spanning several days, and might not involve taking the center of the city.
Senior officials told Fox News that when Marines do roll into the city, they'll search for specific suspects who are thought to be holed up in specific places.
"Our concern is precise. We want to get the guys we are after. We don't want to go in there with guns blazing," said Lt. James Vanzant, 2nd Battalion, 1st Marine Expeditionary Force from Camp Pendleton, Calif.
The Marines and Iraqi security forces were poised to enter the city to arrest suspected insurgents, Vanzant said. "It's an extended operation. We want to make a very precise approach to this. ... We are looking for the bad guys in town," he said.
Defense officials told Fox News that there are some 1,200 Marines dug in around Fallujah, many others have spread out around the surrounding Al Anbar province in raids targeted against individuals known to be causing severe problems for the coalition.
Of the "six or so" individuals targeted in these raids, one source said, "all have been captured." They're thought to have been financiers, recruiters and weapons suppliers for anti-coalition elements, and all are thought to have had connections with the former regime.
Coalition forces mounted 1,566 patrols, conducted 18 raids and captured 42 anti-coalition suspects — all within a 24-hour period spanning Sunday and Monday — Brig. Gen. Mark Kimmitt told reporters in Baghdad Monday.
"These are the first in a series of actions to attack anti-coalition" forces, he said.
Marines imposed a 7 p.m. to 6 a.m. curfew, warning the 300,000 inhabitants to remain indoors.
Iraqi police visited mosques, dropping off Arabic leaflets from the U.S. military, ordering them not to congregate in groups or carry weapons. It instructed Iraqis that if U.S. forces enter their homes, they should gather in one room, and if they want to talk to the troops, they should have their hands up.
Contractor Killers 'Are Specially Targeted'
After the slayings of the Americans on Wednesday, residents dragged the four bodies through the streets, hanging two of their charred corpses from a bridge in scenes that showed the depth of anti-U.S. sentiment in the city.
Marine 1st Lt. Eric Knapp said the coalition will target the killers of the four Americans as well as rebels who have attacked U.S. forces and Iraqi police.
"Those people are specially targeted to be captured or killed," he said.
Senior defense officials stressed that the Fallujah operation wouldn't have happened even if last week's killings and barbaric acts against the four contractors hadn't taken place.
"It was not the coalition that caused the casualties in Fallujah, it is the coalition that's responding to the casualties in Fallujah," Kimmitt said. "We have a responsibility, we have an obligation, to maintain a safe and a secure environment."
U.S. forces are hoping the Iraqis themselves will turn the insurgents in and that Iraqi police will be the ones to arrest and interrogate the suspects.
"This is a psychological objective, not a military one" for the U.S. military, said retired Army Maj. Gen. Bob Scales. "Control Fallujah and I think the insurgency will be kept in control."
Gen. John Abizaid (search), the Centcom leader who oversees the U.S. forces in Iraq, held meetings at the Pentagon Friday with military and intelligence leaders. Changing the situation on the ground in Fallujah — considered the most dangerous city for the coalition — was a central agenda item.
Coalition spokesman Dan Senor told reporters Monday that "there are clearly" foreign fighters and other Baathists still in Iraq leading insurgent activity.
"We will not tolerate that, the Iraqi people certainly will not tolerate that," Senor said. "There's no room for extremists in Iraq … elections will determine who governs Iraq, not mob violence."
Fox News' Bret Baier, Liza Porteus and The Associated Press contributed to this report.