After a week of violence that killed 19 Americans and challenged the authority of Iraq's interim government in vast areas of the country, U.S. commanders launched airstrikes Thursday on two cities controlled by insurgents and sent troops into a third to reinstall a deposed local government.

The Iraqi Health Ministry said at least 43 people were killed and 111 wounded during air attacks on Fallujah, 35 miles west of Baghdad, and Tall Afar, a northern city near the Syrian border. U.S. troops massed outside Tall Afar, in apparent preparation to move in and restore the local government there.

In Samarra, about 65 miles north of Baghdad, U.S. soldiers accompanied deposed city council members across a bridge into the city and stood guard while they elected an interim mayor. The transition was peaceful and conducted under an agreement with community leaders, but insurgents were not required to disarm, according to Army Maj. Neal O'Brien, spokesman for the Army's 1st Infantry Division.

O'Brien said U.S. troops, who have stayed out of Samarra in the nearly three months since insurgents used bombs, kidnappings and other methods of coercion to wrest control from U.S.-installed officials, would continue to help maintain order.

The simultaneous operations in three provinces signaled an aggressive effort to reassert control after the recent spasm of violence. During the past week, a suicide car bomb killed seven U.S. Marines outside Fallujah, heavy gunfire sounded for a day in a Baghdad slum, roadside bombs exploded and two female Italian aid workers were kidnapped in daylight in the capital.

The violence pushed the death toll for Defense Department personnel in Iraq past 1,000 since the conflict began 18 months ago.

U.S. officials and leaders of the interim government contend that re-establishing authority over regions controlled by Sunni and Shiite insurgents is critical to a plan to hold nationwide elections in January.

The Fallujah airstrikes targeted a building occupied by three associates of Abu Musab Zarqawi, a Jordanian linked to al Qaeda, at a time when no other people were in the area, the U.S. military said in a statement.

"The clear and compelling intelligence leading to this mission was derived from multiple Iraqi sources," the statement said. "Terrorists of the Abu Musab al-Zarqawi network have been responsible for multiple acts of terror including the killing of innocent Iraqi citizens, Iraqi Police and Iraqi security forces as well as Multinational forces."

One doctor, Rafi Hayad, said four of those killed were children and two were women, according to the Reuters news agency. U.S. officials offered no information on casualties.

U.S. troops have stayed on the city's periphery since an April agreement was reached after three weeks of fighting. The U.S. military has said it suspects that Zarqawi uses Fallujah as a base to launch attacks against Americans. The car bomb that killed the seven Marines outside the city was the deadliest attack on Americans since April 29.

In Tall Afar, U.S. military officials said the operation was aimed at ridding the city of a "terrorist threat" that had led to "dozens of the attacks" in recent weeks.

The U.S. military denied reports that its forces were stopping ambulances from reaching the city. The ambulances were allowed to enter and exit after being searched, the military said. "This precaution is necessary because terrorists in Tall Afar have used ambulances to move about the city," a statement said.

In a statement Thursday night, the military said the operation was continuing after insurgents took cover in a mosque. The regional government's television station reported military operations would continue "until the city is liberated from outsiders and saboteurs so that peace can be restored," the Associated Press reported.

But Samarra had a peaceful turnover. Members of the city council gathered Thursday morning at a bridge leading across the Tigris River into the city. According to O'Brien, they were met by Col. Randel Dragon, commander of the 2nd Brigade Combat team of the 1st Infantry Division, and Lt. Col. Eric Schacht, commander of the 1st Battalion, 26th Infantry Regiment, and accompanied by U.S. troops.

The city council members then "escorted us into the city," O'Brien said. There was no violence.

Once in Samarra, the council elected an interim mayor who would be replaced after the January elections. U.S. troops and members of the reconstituted 202nd Iraqi National Guard battalion, which effectively dissolved after many of its troops deserted or declined to take part in battle last April, then assessed the condition of eight local police stations, some of which had been bombed by insurgents.

The U.S. troops will stay in Samarra "until the job is done and Iraqi security forces are in position to have control of the entire security situation," O'Brien said. "This is just the first step."

The 1st Infantry Division, which maintained a base on the periphery of the city, treated Samarra as essentially off-limits because of the danger. U.S. officials said the security situation changed after about 50 insurgents were killed in battles with U.S. forces during fighting last month.

O'Brien said local officials and religious leaders then opened negotiations with U.S. commanders. He said the local leaders also held separate meetings among themselves to reach a deal by which the former government would be brought back.