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Coalition forces fired upon a mosque compound in Fallujah that officials said was a safe haven for enemy fighters on Wednesday as U.S. Marines continued their advance into northern areas of the city.

Marines waged a six-hour battle around the mosque with militants holed up inside before a Cobra helicopter fired a Hellfire missile at the base of its minaret and an F-16 dropped a bomb, said Marine Lt. Col. Brennan Byrne.

There is no report of civilian casualties, the military said, disputing earlier witness accounts that as many as 40 people died.

"What we're seeing in Iraq today is a power play between those who favor terrorism and a return to oppression and those who want freedom and self government," Defense Secretary Donald Rumsfeld (search) said at the Pentagon Wednesday. He warned that those who oppose progress "will not be permitted to derail it."

"U.S. forces are on the offense … we will certainly not allow fugitives from Iraqi justice to stop progress for a better life for 25 million Iraqi people," Rumsfeld said. "The United States will stand resolute with the Iraqi people."

The fighting in Fallujah (search) and neighboring Ramadi (search), where commanders confirmed 12 Marines were killed and at least 20 wounded Tuesday, was part of an intensified opposition from some Sunnis and Shiites stretching from Kirkuk in the north to near Basra in the south. At least 60 Iraqis were killed and more than 120 wounded in overnight fighting in Fallujah.

Marines making incursions toward Fallujah's city center on Wednesday battled gunmen in the streets. Mosque loudspeakers blared calls for jihad, or holy war, and women were seen carrying guns in the streets.

Both cities are located in the so-called Sunni Triangle (search) — the area that has proved to pose the most danger to coalition forces that is chock full of Saddam Hussein loyalists. The burst of anti-American violence comes just before Friday's one-year anniversary of the fall of Baghdad to U.S.-led forces.

In other Iraq developments Wednesday:

— Senior defense officials told Fox News of at least two incidents in which Western reporters were kidnapped in two separate cities in Iraq. Two journalists and two security guards were later released.

— Polish troops killed the head of the Karbala office of radical Shiite cleric Muqtada al-Sadr (search) during clashes in the holy Shiite city, Iraqi police said. But Arab networks reported that "a member" — not the head — of al-Sadr's office was killed.

— A U.S. helicopter made a controlled landing in Baquoba after being hit by small-arms fire but no one was injured.

— Operations from the Syrian border to the Baghdad suburbs have resulted in the capture or death of a significant number of anti-Iraqi forces and foreign terrorists, the U.S. military said.

— Reuters reported that one U.S. Marine was killed when his convoy was attacked in Baghdad.

'Everyone in That Mosque Was an Insurgent'

U.S. Marines attacked the mosque compound in Fallujah only after coming under enemy fire from inside the buildings, said Lt. James Vanzant of the 1st Marine Expeditionary Force.

"Everyone in that mosque was an insurgent," Vanzant said, referring to claims that 40 people were killed inside.

U.S. Central Command issued a statement Wednesday afternoon that said one anti-coalition insurgent was killed. Marines used air support to breach a wall several hundred yards away from the actual structure of the Haj Musheen Abdul Aziz Az-Kubaysi (search) mosque after they came under fire.

"They were taking a tremendous amount of fire," U.S. Brig. Gen. Mark Kimmitt (search), a top military official in Baghdad, told Fox News.

"We always observe religious sites. We don't want to make the situation worse by going after a place that has such a significance for the people ... but when a site such as a mosque is clearly used to incite violence ... it loses its protected status."

Fox News' Oliver North received a phone call from a Marine officer in Fallujah, who verified that during a search operation near the mosque, U.S. forces were fired upon by mortars and RPGs from inside the compound. Marines returned fire but purposefully did not hit the mosque.

The wall was intentionally breached so Marines could enter the courtyard around the religious shrine, the officer said. There were no U.S. casualties, he said, nor was there damage to the actual shrine.

"The anti-coalition forces firing from the mosque wrongfully violated the law of war by conducting offensive military operations from a protected structure," the Centcom statement said. "As a result, the mosque lost its protected status and therefore became a lawful military target."

Following the strike, Marines recovered a fully functional mortar from inside the compound.

Kimmitt said military officials believe al-Sadr is hiding in a mosque somewhere in the center of Iraq.

"We think we're making a dent on his forces … the remainder of the country, frankly, is moving on," Kimmitt said.

'Bullets Flying All Over the Place'

In Ramadi, fighting was so intense that commanders went to the unit headquarters to pull people who wouldn't normally fight into the combat, military sources said.

"This is not like any other firefight we've seen so far," military sources in Iraq said. "There are bullets flying all over the place."

Several Iraqis called the coalition tip line to help identify, isolate and combat the insurgents, a U.S. military statement said. When the fighting subsided, the statement said, Ramadi remained under the local Iraqi government's supervision.

Meanwhile, Kimmitt vowed to "destroy" a Shiite militia that, along with Sunni Muslim guerrillas, waged the most extensive fighting since Bush declared the war over in May.

Kimmitt said U.S. forces were trying to hunt down members of the al-Mahdi Army in the mainly Shiite neighborhood of Sadr City (search) in Baghdad, while U.S. and coalition forces were working to prevent militiamen from seizing government buildings and police stations in southern cities.

Kimmitt called on the cleric al-Sadr to surrender. "If he wants to calm the situation ... he can turn himself in to a local Iraqi police station and he can face justice," Kimmitt said.

Although the fighting appears to be mainly by al-Sadr's militia, senior U.S. officials said there is a growing feeling that most of the weekend's attackers were also former regime elements and Baath Party members.

"All the Iraqi people that are watching this understand this. It all comes down to extremism versus moderation," Kimmitt said. "The extremists want to ... take this country back to an authoritarian regime or even worse ... some sort of Talibanization of this country."

Marines this week launched Operation Vigilant Resolve (search) to root out Sunni Muslim guerrillas from Fallujah in retaliation for last week's killing of four American civilian contractors whose bodied were burned, dragged through the streets and hung from a bridge in the city.

Tuesday and Wednesday's casualties could have brought the total since Sunday to about 30 Americans and more than 150 Iraqis killed.

Fox News' Bret Baier, Mike Emanuel, Ian McCaleb, David Piper, James Rosen and The Associated Press contributed to this report.