U.S. and Iraqi troops fought to crush the spreading insurgency in Iraq's third-largest city Tuesday, recapturing police stations and securing Tigris River (search) bridges as they battled to oust fighters who had moved into Mosul as a distraction to the Marine offensive in Fallujah.

Troops met "very little resistance" in securing several of the dozen or so police stations that had been captured by insurgents, the U.S. military command said. Nineveh province's deputy governor said militants blew up the Zuhour police station ahead of the U.S. advance, but the U.S military denied any stations were destroyed.

Loud explosions and gunfire could be heard as U.S. warplanes and helicopters circled over Mosul (search), Iraq's third-largest city with more than 1 million residents.

Mortar shells hit two areas near the main government building in the city center, killing three civilians and wounding 25, hospital officials said. One American soldier was wounded when a car bomb exploded near a U.S. convoy in western Mosul, the military said.

The U.S.-led offensive is aimed at seizing control of the city 225 miles north of Baghdad, where gunmen stormed police stations, bridges and political offices last week. The city's police force was overwhelmed and in many places failed to even put up a fight. Some officers also allegedly cooperated with insurgents.

The operation was launched after U.S. and Iraqi reinforcements were rushed to Mosul. A U.S. Army infantry battalion was recalled from the fighting in Fallujah, 300 Iraqi National Guard (search) soldiers came from garrisons along the borders with Iran and Syria and a special police battalion was sent from Baghdad.

U.S. military spokeswoman Capt. Angela Bowman said the attack began Tuesday as troops closed Mosul's five bridges and American soldiers began securing police stations in the western part of the city.

"We are in the process of securing all of the police stations and returning the police to these stations," she said.

U.S. Marines continued to hunt for fighters hiding in Fallujah, but airstrikes and gunfire waned considerably after a week of heavy fighting that left the Americans in control of the city west of Baghdad that had been the main insurgent bastion.

The U.S. military said it was investigating the fatal shooting of a wounded "enemy combatant" by a Marine in a Fallujah mosque over the weekend. The inquiry was begun after videotaped pool pictures taken Saturday by NBC showed the incident during an operation of the 3rd Battalion, 1st Marine Regiment.

The Marine was removed from the battlefield pending the results of the investigation, the military said.

U.S. aerial missions over Iraq are beginning to slow after a 50 percent jump that accompanied the Fallujah offensive, said Rear Adm. Barry McCullough, commander of the USS John F. Kennedy battle group in the Persian Gulf.

"The operation is starting to wind down now. That doesn't mean there aren't pockets of insurgents and terrorists in Fallujah," McCullough told The Associated Press.

A U.S. soldier was killed and another wounded north of Baghdad on Tuesday when a bomb detonated near their convoy, the U.S. military said.

Stepped-up assaults on insurgents in Fallujah and elsewhere have pushed the U.S. death toll to at least 91 in November, making it the second-deadliest month for American troops since the Iraq invasion in March 2003, Pentagon figures show. The worst month was April, with 135 deaths, when Marines fought fierce battles in Fallujah, only to be withdrawn.

In other violence, a rocket hit a busy commercial district near the government administration building in the northern city of Kirkuk, killing one person and wounding three, Iraqi officials reported. The motive for the attack was not immediately clear.

Meanwhile, hope faded for kidnapped aid worker Margaret Hassan after Al-Jazeera television announced it had a video showing a masked man shooting a blindfolded woman in the head. Hassan's family in London said they believed the longtime director of CARE's operations in Iraq was the victim.

The 59-year-old Hassan, abducted in Baghdad on Oct. 19 by armed gunmen, was the most prominent of more than 170 foreigners kidnapped in Iraq this year. Her captors issued videos showing her pleading for Britain to withdraw its troops from Iraq and calling for the release of female Iraqi prisoners.

In Baghdad, U.S. troops arrested Naseer Ayaef, a deputy head of the Iraqi National Council and a high-ranking member of the Iraqi Islamic Party, said Ayad al-Samarrai, an official in the influential Sunni Muslim political party.

Al-Samarrai contended the arrest was retaliation for the party's criticism of the Fallujah offensive and opposition to security policies of the U.S. command and Iraq's interim government.

There was no comment from U.S. authorities. Prime Minister Ayad Allawi's office said it was demanding that Ayaef be turned over to the government and promised any charges would be investigated fairly.