HADITHA, Iraq (AP) -- Iraqi commanders accompanied by U.S. Marines walked through the streets of this former insurgent stronghold Saturday, trying to convince residents they could safely provide tips about hidden militants in what has evolved from a major military assault into a campaign to break the insurgency's psychological grip on the city.

Men in traditional Sunni Arab robes appeared outside in greater numbers, but still lingered close to their homes in Haditha, a city sloping downward a desert valley toward groves of palm trees along the Euphrates River.

Though insurgents were not on the streets, their presence was evident: Marines said fliers were found threatening those who vote in next weekend's constitutional referendum, and at one mosque a letter from a former policeman was found, begging al Qaeda members for forgiveness for joining security forces.

"We know the enemy is wise and cunning," said Capt. Timothy Strabbing in the 3rd Battalion of Hudsonville, Michigan. "He's watching right now, looking for seams and gaps where he can attack us."

Operation River Gate
An Iraqi army company commander, in his first visit to the city, toured the town, talking to residents and handing out fliers calling on people to provide tips about insurgents.

Operation River Gate began Monday night, when some 2,500 Marines, soldiers and sailors moved in to Haditha and two nearby towns, starting with an air barrage by war planes and attack helicopters that lit the sky. Bridges were taken out, suspected insurgent hideouts were hit, residents were ordered to remain inside.

The troops entering Haditha -- where the military had said insurgents were working freely after largely driving out Iraqi police -- have had relatively few encounters with insurgents.

But the militants have not simply wilted away in the face of the offensive. Instead they have struck back at U.S. forces in their traditional method: by detonating roadside bombs from afar and blending in with an apprehensive population.

Insurgent bombs increasingly sophisticated
Three U.S. soldiers were killed by a roadside bomb Monday and two more by small arms fire Friday in Haqlaniyah, a nearby town targeted in River Gate. Three Marines were killed in a similar, six-day offensive codenamed Iron Fist near the Syrian border that ended Thursday.

Dozens of bombs have been found in Haditha so far, many constructed in increasingly sophisticated and powerful forms.

But now the main task is convincing the approximately 100,000 Sunni Arabs who live in the three towns that they will be safe if they help turn in insurgents -- primarily fellow Sunnis -- and knuckling down on those who sympathize with the militants.

That means the Marines must also wipe away recent history. Skeptical residents pointed out that the Marines left shortly after previous, smaller sweeps in the area, including in August, leaving them behind to lurking insurgents.

"I think they first need to see we're here and then they'll believe we're going to stay," said Capt. James Kimber, of Fountain Hills, Arizona, a company commander in the 3rd Battalion, 1st Marine Regiment. "Then they'll start getting back to their normal lives."

Marines insisted they would stay this time, but few details were provided on the size of the force that would remain.

Kimber, who accompanied the Iraqi commander in his first visit to the city, said Marines were trying to locate former policemen in an effort to reconstitute the force.

Injured civilians
Most residents said they had no water after a roadside bomb was detonated by the military two days earlier, accidentally puncturing a nearby water main. Marines said the main would likely be repaired Sunday.

Others asked that blocked roads be reopened so they could take sick relatives to nearby hospitals. One man held his child in his arms, trying to persuade the squad of Marines and Iraqi officer to let him cross blocked off roads to reach a hospital in the nearby city of Haqlaniyah, also targeted in the offensive.

Marines told him to instead bring his daughter to their base for treatment, but not before Kimber lectured his medic for not bringing sufficient supplies to treat civilians.

The Marines' task of weeding out information on militants is complicated by the changing allegiances of residents, who have waited to see who emerges as the most powerful -- or threatening -- force.

Earlier this week, a cache of weapons, including several bombs ready to be planted with protruding wires, were found buried in a mosque courtyard in Haditha. A day later pro-U.S. messages blared from mosque loudspeakers, urging residents to warn their children about the evil insurgency.

The U.S. military has pinned its hopes on Iraqi troops, who they are slowly integrating into patrols and key operations in Haditha, as they did earlier this year further down the river in the city of Hit, the largest city in the area.

But the Iraqi forces arriving in Haditha reflect internal fissures in the country: the Iraqi commander said only about 10 of over 100 troops in his company were Sunni, a possible point of contention in this Sunni-dominated city. Most were from the Shiite south, said the Iraqi army captain, himself a Sunni Arab. The captain would only give his first name, Ahmed, because he feared his family could be targeted by militants.

Moreover, the introduction of Iraqi security forces in other parts of the country has not ensured safety, so long as the insurgency has been able to regenerate itself. Quiet has mostly taken hold in religiously and ethnically homogenous areas far from this Sunni-dominated region.

Though the firefight was easily won in a matter of hours, the real fight would slowly be fought over the next months and longer, Marines said.

"Instead of being intimidated by the insurgents, it's our opportunity to build trust (and) social capital with the local population to provide us with key information to ultimately protect them," said Strabbing. "We're at the fetal stages of this. This takes time."