U.S.-led coalition forces struck a suspected terrorist safehouse in Fallujah on Friday, hoping to cripple Abu Musab al-Zarqawi's (search) network.

U.S. officials estimated that 20 to 25 people in the house at the time were killed. It was the third airstrike in a week.

"Coalition forces conducted another strike on a known Zarqawi network safehouse in southeastern Fallujah, based on multiple confirmations of Iraqi and coalition intelligence," said Brig. Gen. Mark Kimmitt (search).

Kimmitt said precision weapons were used to target and hit the suspected terrorist safehouse.

"It underscores the coalition's continued resolve, in partnership with the Iraqi forces, to destroy terrorist networks within Iraq," Kimmitt said. "Wherever and wherever we find elements of Zarqawi's network we will attack and destroy them."

The Jordanian-born Zarqawi claimed responsibility for coordinated attacks in other Iraqi cities that killed more than 100 people Thursday — less than a week before Iraq's new government takes power. Insurgents set off car bombs and seized police stations in an offensive aimed at creating chaos before the handover.

He has also had a hand in numerous other attacks against the U.S. and the coalition, and is suspected to have carried out the grisly beheading last month of American contractor Nicholas Berg.

"Wherever and whenever we find elements of the Zarqawi network, we will attack them," a military statement said of the strike.

U.S. officials did not indicate how they determined the figure of 20 to 25 dead.

In a report from Fallujah (search), Al-Jazeera television said four U.S. missiles struck a vacant house in the eastern part of the city, injuring four residents of a nearby home.

In Baghdad, the country's new leadership, due to assume sovereignty in five days, promised stern action against the insurgents, claiming much of the unrest was directed by foreigners but offering no proof.

"Our culture, our customs have been destroyed," interim Defense Minister Hazem Shaalan said. "The time has come for a showdown."

Earlier Friday, U.S. tanks and armored vehicles maneuvered on a highway near the edges of Fallujah, firing in all directions, while armed men in an eastern suburb returned fire, witnesses said. Seven people died in two days of fighting there, hospital officials said.

A roadside bomb exploded in a residential neighborhood in Baghdad, killing one Iraqi policeman and wounding another, police said.

In Thursday's coordinated attacks, insurgents set off car bombs and seized police stations in an offensive aimed at creating chaos just days before the handover of power to a new Iraqi government. U.S. and Iraqi forces regained control in heavy fighting, but the day's violence killed about 100 people, most of them Iraqi civilians.

Three U.S. soldiers were among the dead. At least 320 people were wounded, including 12 Americans.

As the situation worsened, Iraq's interim vice president warned that a drastic deterioration in the country's security could result in the implementation of emergency measures or martial law — however undesirable that may be in a democratic society.

"Announcing emergency laws or martial law depends on the nature of the situation. In normal situations, there is clearly no need for that (step)," Ibrahim al-Jaafari, a Shiite and member of the Islamic Dawa Party (search), told The Associated Press in an interview.

"But in cases of excess challenges, emergency laws have their place," he said, adding that any such laws would fall within a "democratic framework that respects the rights of Iraqis."

Mosul residents said the northern city was tense Friday, with a marked increase in the number of police on the streets. Fewer people ventured out to markets for fear of more attacks.

Elsewhere, three mortar shells exploded early Friday near an oil pipeline damaged last week by sabotage, police Capt. Mushtaq Talib said. The latest explosion caused no damage, Talib said.

Iraq's new leaders recently have suggested the possibility of at least partial martial law in some hotspots around the country as a way of stemming the violence. It is unclear, however, whether U.S. officials would go along with the idea.

The U.N. Security Council (search) resolution approved this month gives the United States a primary security role in Iraq even after the transfer of sovereignty Wednesday.

U.S. and Iraqi forces regained control in heavy fighting and American forces set up checkpoints around Iraq to intercept weapons, guerrillas and bombs. They fear that al-Zarqawi, the militant who claimed responsibility for the offensive, plans a string of car bombings in Baghdad, said Col. Michael Formica, commander of the 1st Cavalry Division's 2nd Brigade.

"There is clearly a transnational threat, as represented by al-Zarqawi, and that threat appears — based on what we've seen in Fallujah and Mosul today — to want to bring the attack to Baghdad," Formica said Thursday.

A large number of victims from Thursday's attacks were killed in simultaneous car bombings in Mosul, but some also died as U.S. troops battled the guerrillas.

"We underestimated the nature of the insurgency that we might face during this period, and so the insurgency that we are looking at now ... has become a serious problem for us," Secretary of State Colin Powell (search) told the British Broadcasting Corp.

The U.S. military responded with heavy firepower, dropping 11 500-pound bombs and a 2,000-pound bomb.

The assaults were launched Thursday morning, when black-clad guerrillas attacked police stations and government complexes in Baghdad, Baqouba, Mosul, Ramadi and Mahaweel. U.S. troops and insurgents traded heavy fire on the outskirts of Fallujah, where explosions were also heard early Friday.

The heaviest fighting was in Baqouba, northeast of the capital, where guerrillas shot their way into a government office complex, seized two police stations and destroyed the home of the provincial police chief. The stations were recaptured later, said Maj. Neal O'Brien of the 1st Infantry Division on Friday.

Two American soldiers died in the Baqouba fighting, the 1st Infantry Division said.

Insurgents also attacked a police station in a Baqouba suburb late Thursday, killing three officers and injuring one, said Dr. Nassir Jawad, who is in charge of the Baqouba morgue. Isolated skirmishes were also reported into Thursday evening, O'Brien said Friday.

But the day's worst bloodshed came in Mosul — the country's northern metropolis often touted as a success story in restoring order in Iraq — where the U.S. military said 62 people were killed, including a U.S. soldier, and more than 220 people were wounded.

Most died when at least four car bombs rocked the police academy, two police stations and the al-Jumhuri hospital.

U.S. troops recaptured the Sheik Fathi police station in a hail of gunfire, and Iraqi troops raided a nearby mosque used by insurgents, the U.S. military said. Mosul's governor imposed an overnight curfew.

Al-Zarqawi's followers claimed responsibility for Thursday's attacks in a statement posted on an Islamic Web site often used by his Tawhid and Jihad movement. The statement said the "occupation troops and apostates" — meaning Iraqi police — "were overwhelmed with shock and confusion."

Al-Zarqawi earlier claimed responsibility for the kidnappings and beheadings of American businessman Nicholas Berg and South Korean hostage Kim Sun-il, and an audiotape released Wednesday purporting to be by al-Zarqawi threatened to kill Iraq's prime minister.

Analysis showed it likely was al-Zarqawi's voice, a CIA official said.

American and Iraqi officials insisted the transfer of power would proceed as planned. On Thursday, the coalition turned over the last 11 government ministries to Iraqi officials.

During the handover ceremony, interim Prime Minister Iyad Allawi (search) said the attacks were "only acts of disturbances conducted by cowards" meant "to foil the democratic process."

The Associated Press contributed to this report.