Insurgents fought U.S. troops in running street battles in the capital Saturday, assassinated three Iraqi officials and their driver and detonated a car bomb in Baghdad's Liberation Square, a grim cadence that some Iraqis feared signaled the onset of a rebel offensive in the capital. In northern Iraq, the U.S. military discovered the bodies of nine slain Iraqi soldiers.

There were moments of fleeting optimism amid the bleakness Saturday: A woman abducted last month was freed and returned to her native Poland, and the United States and Germany reached a tentative deal to forgive as much as four-fifths of Iraq's crushing $122 billion foreign debt.

But most of the day's news fit a familiar pattern in a country reeling from relentless violence. Acting on a tip, U.S. troops discovered the bodies of the Iraqi soldiers in an open expanse off a main road in Mosul about a mile from the Tigris River. All nine had been shot in the back of the head, said Lt. Col. Paul Hastings, an Army spokesman in the northern Iraqi city.

The men, who were not in uniform, were identified as members of an army unit stationed at the Kisik military base, about 30 miles west of Mosul, Hastings said. Their discovery follows the recovery of four beheaded bodies on Thursday, he said. Like the soldiers, they were in civilian clothes but have yet to be identified.

"It tells you something about the enemy and the level of extremism that possesses these people to do that," Hastings said. About 2,500 U.S. troops entered Mosul this week to try to staunch a surge of rebel attacks. "It's obviously very disturbing, to say the least."

The scenes in Baghdad sent a shudder through the capital, as fighting emptied streets and unfurled columns of black smoke over the Sunni Muslim neighborhood of Adhamiya. Overhead, AH-64 Apache attack helicopters buzzed through a cloudless sky, while in the streets, men with rifles and rocket-propelled grenade launchers hurried through the neighborhood.

The U.S. military said one American soldier was killed and nine were wounded in an attack at 7 a.m., when insurgents detonated improvised mines and fired rifles and rocket-propelled grenades at their unit. In the hours that followed, clashes erupted in at least four Baghdad neighborhoods, with most of the fighting centered in Adhamiya.

Roads there were closed, some barricaded with tires and blocks of concrete, forcing cars the wrong way down streets to escape the fighting. The police station came under attack, and firetrucks tried to extinguish blazes in several shops in Antar Square. Footage broadcast by Arab satellite networks showed a U.S. Humvee in flames.

Ambulances raced through the neighborhood with sirens blaring, and smoke blocked the view of the Royal Cemetery, distinguished by a turquoise-domed tomb for members of the Hashemite family that ruled Iraq until the monarchy's fall in 1958.

The clashes in Adhamiya came a day after Iraqi troops backed by U.S. soldiers raided the most revered Sunni mosque in Baghdad, setting off stun grenades, arresting dozens and leaving at least two people dead. The raid was part of a U.S. and Iraqi crackdown on clerics perceived as supporting the insurgency, but it ignited anger in a neighborhood that has smoldered almost since the start of the U.S. occupation in 2003.

A U.S. general familiar with the operation, speaking on condition of anonymity, said the raid on the Abu Hanifa mosque was planned by U.S. Special Forces, working with Iraqi allies. While several officers stressed that U.S. forces would not allow insurgents sanctuary anywhere, even in intensely sensitive sites such as mosques, the general said that he believed the raid could have been less provocative. The operation was carried out right after Friday prayers, often a time when emotions are running high.

To many in Baghdad, the fighting was redolent of the days during the U.S. invasion, when the streets were largely deserted by dusk. On Saturday, with electricity in especially short supply, swaths of the city were cast in darkness by nightfall.

"They said they are bombing Adhamiya, and my mother is there alone. Why is this happening?" asked Mary Polis, 13, who was visiting relatives across town and unable to return to her family's home. Her relatives said her father was wounded in the right shoulder by stray gunfire Saturday morning, when the fighting was most intense.

Some residents complained that the U.S. attack last week on Fallujah, a city along the Euphrates River about 35 miles west of the capital, had unleashed fighting that has raged in regions north and west of Baghdad and in the capital itself. Those sympathetic to the insurgency equated the U.S. attack with striking a hornet's nest. Those opposed used Iraqi slang to describe the rebels. "Inchalabow," they said: to become like wild dogs.

On Saturday, the attacks stretched across the tattered capital. In Liberation Square, at the end of Saadoun Street, a busy commercial thoroughfare, smoke billowed over central Baghdad after a suicide bomber blew up his vehicle just after noon, killing an Iraqi civilian, wounding another and setting several vehicles on fire.

In the neighborhood of Qadisiya, masked men driving in an Opel attacked the car of Amal Abdel Latif, an adviser to the Public Works Ministry. She was killed, along with her secretary, driver and another employee, said Alan Aref, a ministry spokesman.

The offensive against Fallujah was designed to eradicate what had become a virtually independent fiefdom of rebels and, in the eyes of many Iraqis, the base for a wave of kidnappings, beheadings and car bombings that has repulsed many here.

U.S. officials estimated that 1,200 fighters were killed in the city, once home to 300,000 people, but the insurgents' main leaders -- Abdullah Janabi, Omar Hadid and Abu Musab Zarqawi -- appear to have escaped.

The U.S. general who oversaw the capture of former Iraqi president Saddam Hussein last December predicted that Zarqawi's arrest would prove more difficult.

With Hussein, "after the fall, there was no organization, he was fleeing for his life, whereas I think Zarqawi is a little more organized. . . . He has a more organized group around him than Saddam Hussein," Army Lt. Gen. Raymond T. Odierno told reporters traveling with Secretary of State Colin L. Powell. "That's what makes it a bit more difficult." Powell attended a summit with President Bush in Santiago, Chile, Saturday before heading for the Middle East.

Beyond Baghdad, fighting continued in the turbulent region known as the Sunni Triangle. Another day of clashes erupted in Ramadi, west of Fallujah, where U.S. forces sealed roads into the city and flew helicopters low overhead. The Associated Press, quoting hospital officials, said nine Iraqis were killed and five were wounded.

Mortar shells were fired at the U.S. base in Baqubah, northeast of the capital, residents said, and guerrillas fought U.S. troops in Qaim, a restive town near the border with Syria.

A militant group, the Army of Ansar al-Sunna, posted a video on a Web site that it said showed one of its members shooting dead two men from the government-allied Kurdistan Democratic Party. It accused Kurds of helping fight insurgents in Mosul.

The freed Polish woman, Teresa Borcz Khalifa, spoke to reporters in Warsaw on Saturday but declined to say how she was freed or to give any details.

Prime Minister Marek Belka said she arrived in the Polish capital the night before.

"It was a very joyous moment for me," said Khalifa, 54, whose abductors had demanded Polish troops withdraw from Iraq. "I feel well, very well."

Khalifa, who holds dual Polish-Iraqi citizenship and is married to an Iraqi, said she was treated well and called her abduction "very well organized." More than 170 foreigners have been kidnapped in Iraq. At least 34 have been killed, including Margaret Hassan, 59, an aid worker for CARE International abducted last month who had British, Irish and Iraqi citizenship.

In Berlin, after a months-long U.S. effort, Germany and the United States agreed to a proposal for writing off as much as 80 percent of Iraq's foreign debt. The deal still needs approval from the Paris Club of creditor nations, to which Iraq owes about a third of its debt.

Staff writers Robin Wright in Santiago, Chile, and Bradley Graham and special correspondents Bassam Sebti and Naseer Nouri in Baghdad contributed to this report.

An Iraqi chants near the wreckage of a car bombing in Baghdad. Insurgents mounted attacks in at least four areas of the capital and in several other cities.A U.S. soldier retreats from a crowd of Iraqis chanting anti-government and anti-U.S. slogans after a car bombing in Baghdad. The blast killed one person.Teresa Borcz Khalifa, who was taken hostage last month, said in Warsaw after her release that her abduction was "very well organized."