In a bloody surprise attack, the U.S. military launched precision weapons into a poor residential neighborhood of Fallujah on Saturday to destroy what officers described as a safe house used by fighters loyal to Abu Musab Zarqawi and perhaps, at times, by the fugitive terrorist leader himself.

Residents said about 20 people were killed, including women and children, despite a cease-fire with U.S. occupation forces that has brought relative peace for the last six weeks to the rebellious city 35 miles west of Baghdad. Images from the site of the blast showed two collapsed houses, with people in white robes picking through the rubble looking for buried victims and lost property.

"This leads to nothing but more confrontation with the enemy," Abdullah Janabi, head of Fallujah's Mujaheddin Council, declared in an interview with the al-Jazeera satellite television network.

A statement issued by Army Brig. Gen. Mark Kimmitt, the spokesman for U.S. military forces in Iraq, said it was not known whether the elusive Zarqawi was inside the house at the time of the 9:30 a.m. attack but that "multiple confirmations of actionable intelligence" indicated that several of his operatives were present. Kimmitt said secondary explosions lasting 20 minutes pointed to the presence of a large store of munitions and explosives in the targeted building.

Zarqawi, a Jordanian national whom U.S. officials have linked with the al Qaeda network of Osama bin Laden, has been cited by U.S. occupation authorities as one of the leaders of a relentless campaign of bombings and assassinations being waged against the occupation and Iraqis who cooperate with the U.S.-sponsored Iraqi interim government.

"Wherever and whenever we find elements of the Zarqawi network, we will attack them," Kimmitt's statement said.

A senior U.S. military official said he did not dispute the casualty toll given by Fallujah residents, who also said two dozen people were injured in the attack. The Reuters news agency reported that 22 new graves were dug at Fallujah Martyrs Cemetery.

But the official said most of those killed and wounded were inside the two buildings destroyed by the U.S. attack, suggesting that they were not bystanders, and Kimmitt's statement said U.S. planners had decided the high-quality targets were worth the risk of civilian bloodshed.

"This was not an attack on the people of Fallujah, but against a known safe house," the statement said. "It is standard operating procedure to conduct a detailed collateral damage estimate prior to approval of this type of mission. The collateral damage estimate was within permissible limits, and this operation was within standing rules of engagement."

Fallujah has been under the control of loosely organized Islamic militiamen since early May. Their authority has been largely unopposed despite the presence of the 1,700-member Fallujah Brigade, a peacekeeping force commanded by former Iraqi army officers in cooperation with Marine forces assigned to the area.

U.S. forces and Fallujah militiamen fought tough, bloody engagements through most of April, after four U.S. contractors were killed and their bodies burned and mutilated on March 31. Several hundred Iraqis were killed in the clashes, which included U.S. airstrikes that also inflicted civilian casualties. On Thursday, Human Rights Watch called for an investigation of a confrontation in which the rights group said U.S. troops fired into a crowd of protesters on April 28 and 30, 2003.

The city of 300,000, lying in the area known as the Sunni Triangle because of its predominantly Sunni Muslim population, was long known as a stronghold of former president Saddam Hussein's Baath Party and a source of tribal support for his rule.

Against that background, Gen. Mohammed Abdullah Mohammed Shehwani, who heads Iraq's new National Intelligence Service, pressed visiting Deputy Defense Secretary Paul D. Wolfowitz in a meeting Friday not to renew U.S. attacks on Fallujah. As with Shiite Muslim militiamen in Najaf, 90 miles south of Baghdad, many Iraqi political figures cooperating with the U.S. occupation have urged political solutions rather than armed confrontation with anti-occupation fighters.

But U.S. military officers have been disappointed with the Fallujah Brigade's lack of control. In particular, they have complained that those responsible for killing and mutilating the U.S. contractors have not been turned over and that foreign fighters have not been arrested and handed to occupation authorities.

U.S. officials have said they believe that foreign terrorists have found refuge in Fallujah, including Zarqawi on occasion, and are helping organize the attacks against U.S. soldiers, particularly car bombs steered to their targets by suicide drivers.

"He's had a number of locations," a senior U.S. military official said of Zarqawi after the strike on Saturday. "This may have been one of the locations where he's at. . . . We just don't have any evidence."

In addition to the U.S. attack in Fallujah, U.S. troops battled insurgents near Baqubah, 30 miles northeast of Baghdad, for the fourth day, the military official reported. One U.S. soldier and several Iraqis have been reported killed in those clashes.

Meanwhile, in what appeared to be a new development in the nearly 15-month-old U.S. occupation, about 500 women staged a demonstration against violence in Sadr City, a Shiite Muslim neighborhood in eastern Baghdad that has been the scene of repeated clashes between militiamen and U.S. occupation troops.

Draped in mourning veils, the women marched to the offices of Moqtada Sadr, the young cleric who has been leading the uprising against U.S. troops, and then back again through the streets of the slum neighborhood.

"The people who pay for the violence are the women," said Salama Khufaji, a former Governing Council member whose brother was assassinated by insurgents in late May. "We want a stop to the violence, the U.S. to leave the neighborhood and a reactivation of reconstruction projects like water and sewage."

Mourners leave a Fallujah cemetery after burying Iraqis killed in an attack on a suspected refuge for insurgents in the city. A U.S. statement said, "This was not an attack on the people of Fallujah, but against a known safe house."