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The skies above Fallujah lit up for a second night in a row Wednesday as U.S. forces mounted a strategic strike in the Iraqi city that has a strong anti-American insurgent presence.

American forces decided to delay potentially dangerous patrols into the besieged city.

The violence, carried on live television with images of fiery destruction, came as the United States was under increasing international pressure to prevent a revival of the bloodshed seen in the city west of Baghdad during the first two weeks of April.

"Violent military action by an occupying power against inhabitants of an occupied country will only make matters worse," Secretary-General Kofi Annan (search) said. "It's definitely time, time now for those who prefer restraint and dialogue to make their voices heard."

Commanders in Iraq said the Marines were responding to guerrilla attacks and that the military was sticking to a more than two-week-old halt in offensive operations to allow negotiations.

"Even though it may not look like it, there is still a determined aspiration on the part of the coalition to maintain a cease-fire and solve the situation in Fallujah by peaceful means," Brig. Gen. Mark Kimmitt (search) said in Baghdad.

"What's going on are some terrorists and regime elements have been attacking our forces, and our forces have been going out and killing them," Defense Secretary Donald H. Rumsfeld (search) testily told lawmakers in Washington.

Guerrilla attacks broke out in at least three neighborhoods of Fallujah that had been relatively quiet during the past three days. And the U.S. response intensified: when a Marine was wounded, warplanes dropped 10 laser-guided bombs — most of them 500-pound bombs but at least one 1,000 pound — on buildings that were the source of guerrilla fire, Lt. Col. Brennan Byrne said.

At least twice, AC-130 gunships opened up on guerrilla positions with their heavy cannons.

The bombs were dropped when insurgents attacked multiple Marine positions outside the city, senior military officials told Fox News, and they brought a swift end to the action. Officials said there have been "more than a dozen" violations of the cease-fire in and around Fallujah in the last 24 hours.

Throughout the day, the sound of each battle was heard — the rattle of gunfire and the thud of mortars — then came the noise that often marked Marine strikes to put an end to the fight: heavy explosions, raising flames and palls of smoke.

Guerrillas fired on a train station just outside the city's northern edge, prompting a battle in the Golan neighborhood, an insurgent bastion. Fighting also erupted on the northeast, southeast and in the center of the city.

The extent of the battle was difficult to gauge. Witnesses reported at least 25 buildings wrecked by fighting. Hospitals only counted 10 wounded Iraqis, but ambulances could not reach areas where fighting was going on, and residents reported large numbers of dead and wounded.

At the White House, President Bush said "most of Fallujah is returning to normal."

"There are pockets of resistance and our military, along with Iraqis, will make sure it's secure," he said.

The strikes in Fallujah did not represent a full-out offensive on the city, military officials said. But "we’re more than prepared to start a complete military offensive" if negotiations on a fragile cease-fire falls apart, Kimmitt told Fox News.

But the fighting was causing international concern. Escalating violence in the Middle East prompted already nervous investors to sell stocks sharply lower Wednesday, sending the Dow Jones industrials down more than 110 points.

Late in the day, Byrne announced that Marine patrols into the city due to start Thursday had been delayed a day.

The United States decided over the weekend to send in the patrols of Marines and Iraqi security forces to establish a semblance of control over the city.

But with tensions rising, Marines moving on foot through the city streets would almost inevitably draw guerrilla attacks — which could then trigger heavier fighting.

Several families were seen fleeing the city Wednesday during the battles, the latest to puncture a tattered cease-fire in Fallujah.

"I was pinning some hope on the truce. The American air bombing dashed my hopes," Ali Muzel said as he escorted his wife and five children to Baghdad.

A third of the city's 200,000 residents fled earlier.

Operations Outside Fallujah

Marines are conducting operations, sometimes in units as large as 5,000 to 6,000 Marines, in towns to the immediate south of Fallujah, as well as western areas stretching toward the Syrian border, senior military officials told Fox News.

That area was where U.S. forces found and destroyed a makeshift weapons factory. In one day, Marines discovered and disabled five enemy anti-aircraft guns, identified as Zeus 23s, which are nearly useless against U.S. fixed-wing aircraft but are deadly against ground targets. Sources told Fox News that Marines have taken fire from similar weapons located inside Fallujah.

Other operations outside Fallujah continue to net counterfeiters, people providing financial support to the enemy fighters and weapons stocks. "Defensive positions" in areas other than Fallujah have also been identified and neutralized, officials told Fox News.

Negotiations are ongoing with four different Iraqi groups that are directly tied to significant segments of the Fallujan population, Fox News has learned. They are promising cooperation and intelligence information on the enemy fighters' hideouts, especially those of foreign fighters, sources with intimate knowledge of the situation in Fallujah said.

The Iraqi groups apparently are promising to cooperate with Iraqi security forces and Marine patrols as they eventually move through the streets.

U.S. and Iraqi forces were expected to begin joint patrols on Thursday but will be delayed a day to allow more training.

"No one is under any illusions that these dead-enders are just going to throw down their weapons and walk away. That's not going to happen," one defense official told Fox News.

"With every day that goes by — the intelligence gets better, the battle plan gets better — the Marine commanders are 'preparing the battlefield' for their future action ... and they are not in a rush," another official said.

Fox News has learned that about a dozen sheiks are traveling to Fallujah Thursday for a peace conference. Coalition leaders are calling this a significant event, adding that they believe the sheiks are going to urge militants to lay down their weapons.

"We certainly have to allow a process to play out where we did everything we could to avoid what would be an onslaught in Fallujah … and most certainly create an explosion of anger against us. In the end, we have to win the hearts and minds," said Ambassador Dennis Ross, a Fox News foreign affairs analyst.

"In the end, those people who are holding Fallujah hostage cannot be … successful."

Across Iraq, attacks are down, compared with the first two weeks of April, as U.S. officials try negotiate solutions for Fallujah and with militiamen loyal to radical Shiite cleric Muqtada al-Sadr in the south. But violence still flares regularly.

A U.S. soldier was killed in an ambush Tuesday near the northern city of Tel Afar, the military reported.

The soldier's death brought to 116 the number of Americans killed in combat this month, the bloodiest month for U.S. forces in Iraq. At least 725 U.S. troops have died in Iraq since the war began in March 2003. Up to 1,200 Iraqis also have been killed this month.

Also Wednesday, a senior U.S. official said investigators have recommended administrative punishment for a number of commanders after allegations that prisoners were abused at Baghdad's Abu Ghraib prison. The official, speaking on condition of anonymity, would not give details on the recommended punishments or say how many commanders faced action.

Six soldiers at the prison face criminal charges, Kimmitt said.

Saddam Hussein's 67th birthday was Wednesday, his first in U.S. detention since being captured in December. In his hometown of Tikrit, there were no apparent signs of celebration, and schools and universities were closed.

In southern Iraq, gunmen ambushed a Ukrainian convoy outside the city of Kut on Wednesday. Two coalition soldiers were killed, Kimmitt said.

Shiite militiamen loyal to al-Sadr drove Ukrainian peacekeepers out of Kut earlier this month, but U.S. troops then swept into the city, pushing out most militiamen.

U.S. troops seek to capture al-Sadr and suppress his militia. On Wednesday, they began gradually expanding operations outside their base in the holy city of Najaf. Soldiers set up checkpoints on the road outside the base — the main route between the center of Najaf and neighboring Kufa.

Another checkpoint was established on a bridge outside Kufa, near the site of a battle Monday in which the military reported 64 Iraqis were killed. Najaf hospitals reported only 37 people killed.

The military has promised to stay away from sacred Shiite sites at the heart of Najaf. The U.S. base is about three miles from the shrines.

Fox News' Bret Baier, Ian McCaleb and The Associated Press contributed to this report.