Insurgents stormed two police stations Sunday in the strife-ridden city of Mosul (search), killing at least six Iraqi troops as attacks spread throughout Sunni Muslim areas following the U.S.-led assault on Fallujah (search).

Marines found the mutilated body of a Western woman as they searched for militants still holding out in Fallujah, the former Sunni insurgent stronghold. The woman could not be immediately identified, but a British aide worker and a Pole are the only Western women known to have been taken hostage.

At least 38 American troops and six Iraqi soldiers have been killed in the fighting in Fallujah. The number of U.S. troops wounded is now 275, though more than 60 have returned to duty. U.S. officials estimated more than 1,200 insurgents were killed in the weeklong fighting.

"The perception of Fallujah being a safe haven for terrorists, that perception and the reality of it will be completely wiped off before the conclusion of this operation," said Lt. Gen. John Sattler, commander of the 1st Marine Expeditionary Force (search).

U.S. forces have spread throughout the city although it could take several more days of fighting before the city is secured, American officials said. U.S. forces on Sunday attacked a bunker complex in southern Fallujah where they discovered a network of steel-reinforced tunnels filled with weapons, an anti-aircraft artillery gun, bunk beds, a truck and a suspected weapons cache, according to a statement from the U.S. military.

U.S. aircraft attacked insurgents hiding "in numerous buildings throughout the city," the statement added.

Fighting in Fallujah was ebbing, but insurgent attacks appeared to escalate elsewhere in Sunni Muslim areas of central and northern Iraq.

Saboteurs set fire Sunday to four oil wells in Iraq's northern fields, setting off successive explosions in Khabbaza, 12 miles northwest of Kirkuk, oil officials said.

Heavy explosions rattled central Baghdad near the Palestine and Sheraton hotels after nightfall Sunday, followed by bursts of sporadic gunfire. The U.S. military said initial reports indicated rockets or mortars had struck the area, killing two Iraqis and wounding another.

About an hour later, about four more large explosions rocked the Green Zone, headquarters of the U.S. and Iraqi leadership. At least one private security guard was killed. Clashes were also reported on Haifa Street, a center of insurgent support in the heart of the capital.

More than a dozen insurgents attacked the Polish Embassy in Baghdad with automatic weapons Sunday, and embassy guards returned fire in an exchange that lasted for a half hour, a Polish Foreign Ministry spokesman said in Warsaw. No one was reported killed or wounded.

In Mosul, where an uprising broke out last week in support of the Fallujah defenders, militants raided two police stations, killing at least six Iraqi National Guards and wounding three others. One insurgent was killed and three others were wounded before Iraqi security forces regained control of both stations, witnesses said.

Insurgents also set fire to the governor's house, destroying it and damaging his car in northern Mosul. Governor Duraid Kashmoula also said the curfew will continue to be imposed on the city from 4:00 p.m. to 6:00 a.m. in the morning.

A gunbattle erupted Sunday between militants and U.S. troops in the main market in the northern town of Beiji, killing at least six people and wounding 20 others, according to witnesses.

The clash followed an attack in Beiji against American soldiers, who responded with tank rounds and Hellfire missiles, the U.S. military said.

A dozen explosions rocked an American base in the western part of Ramadi, about 30 miles west of Fallujah, after insurgents fired missiles. Witnesses reported seeing flames and smoke billowing from the base.

One U.S. soldier was injured when a suicide bomber blew up his car near a U.S. convoy traveling between Balad and Tikrit, the military said. A Bradley fighting vehicle was damaged by a roadside bomb in Baghdad, injuring one soldier, the military said.

One Marine and an Iraqi soldier were hurt when five mortar shells struck a checkpoint outside Fallujah.

In an interview with Iraqi television Sunday, interim Prime Minister Allawi defended his decision to order the attack on Fallujah, saying he decided to strike after security forces arrested "two very important" terrorist organizations. He did not elaborate.

Allawi said up to 400 insurgents have been captured, including fighters from Syria, Saudi Arabia, Afghanistan and Morocco but he gave no figures.

Despite the ongoing violence, Allawi ordered Baghdad International Airport to reopen Sunday and opened all but one border crossing with Syria. They were closed under a state of emergency announced Nov. 7 on the eve of the Fallujah attack.

In Fallujah, Marines reopened the infamous bridge over the Euphrates River where Iraqis strung up the charred bodies of two American contractors in March. The brutal slaying and mutilation of the four Blackwater Security Consulting employees touched off a Marine assault in April.

That fight was halted but U.S. forces attacked again this week, retaking Fallujah and its bridge from rebels.

"It's symbolic, because the insurgents closed the bridge and we reopened it," said Maj. Todd Des Grosseilliers, of the 3rd Battalion, 5th Marines before Marines rolled away a coil of concertina wire and crossed the span over the Euphrates River on foot.

On Sunday, Marine and Army units were still battling small bands of militants scattered in buildings and bunkers across the Sunni Muslim stronghold. Behind them, Iraqi troops were painstakingly clearing weapons and fighters from every room of Fallujah's estimated 50,000 buildings.

ABC pool video footage showed Marines continuing to search door-to-door, blowing the gates off houses with explosives. A bit of bright color stood out on one of the city's ubiquitous gray, rubble-strewn streets — a pink dress on the body of a small child crumpled next to the curb.

Sunni Muslim militants have cut a swath of terror across the country with a string of recent high-profile kidnappings.

The disemboweled body of the woman was wrapped in a blood-soaked blanket on a street in Fallujah, Marines said. Margaret Hassan, 59, director of CARE international in Iraq, and Teresa Borcz Khalifa, 54, a Polish-born longtime resident of Iraq, were abducted last month but the body could not be identified without further tests.