U.S. troops engaged in heavy combat Tuesday with insurgents in the Sadr City section of Baghdad, leaving at least 25 Iraqis and one American soldier dead in the stronghold of rebel Shiite Muslim cleric Moqtada Sadr.

The U.S. military Tuesday also reported the deaths of four other soldiers in separate incidents in and around Baghdad, bringing to 12 the number of American troops killed in Iraq in the past two days.

In another incident that unsettled the capital, gunmen stormed a building in central Baghdad and abducted two Italian women working for a humanitarian aid agency, along with two Iraqis, news services reported. The Italian women worked for a group called "Bridge to Baghdad" that has been involved in water projects and school construction. The two kidnapped Iraqis reportedly included a woman who worked for another Italian aid agency and a man employed as an engineer for Bridge to Baghdad.

More than 100 foreigners and Iraqis have been kidnapped so far this year, but most of the abductions have taken place outside Baghdad.

As the fighting in Sadr City intensified Tuesday morning following overnight clashes, U.S. tanks moved into the vast slum of more than 2 million people and warplanes flew overhead. Bradley Fighting Vehicles and other armored personnel carriers occupied key intersections in the neighborhood.

U.S. military officials said the fighting began when Sadr's militia attacked U.S. soldiers on routine patrols, killing one American and wounding at least five others. A military spokesman said the fatality occurred in an attack in which insurgents fired rocket-propelled grenades. Such attacks took place several times overnight and Tuesday morning, and several roadside bombs were detonated in Sadr City in efforts to kill or maim U.S. troops, officials said.

"We just kept coming under fire," U.S. Army Capt. Brian O'Malley told the Associated Press.

A spokesman for Sadr in Baghdad, Sheik Raed Kadhimi, blamed the fighting on what he described as intrusive U.S. incursions into the neighborhood and attempts to arrest Sadr's followers.

"Our fighters have no choice but to return fire and to face the U.S. forces and helicopters pounding our houses," Kadhimi said in a statement, the AP reported.

The violence is the first major battle between U.S. forces and Sadr's Madhi Army militia since both sides stepped away from a confrontation in the holy city of Najaf late last month under a cease-fire brokered by a senior Iraqi religious leader. On Aug. 30, Sadr announced through aides that he was planning to participate in Iraq's political development and ordered his militia to suspend attacks on U.S. and Iraqi forces.

Saad Amili, a spokesman for the Iraqi Health Ministry, said at least 25 people were killed and 145 were wounded in the clashes in Sadr City.

In the other fatal incidents, the U.S. military said that three of the soldiers died as a result of roadside bomb attacks in and around Baghdad on Monday and Tuesday, and a fourth was mortally wounded in an unspecified attack in the capital Monday afternoon. Identities of the latest casualties were not immediately released.

A witness said one U.S. soldier who died was shot by a sniper from the roof of a school in the western Baghdad suburb of Ghazaliya while guarding the wreckage of a fuel convoy hit by a rocket propelled grenade.

The latest deaths bring to at least 993 the number of U.S. military members who have been killed in Iraq since the U.S. invasion in March 2003.

In another incident Tuesday, a roadside bomb exploded near a convoy carrying the Baghdad governor and others in a western suburb of the city. The governor was not injured, but two other people were killed, although it was not immediately clear if they were part of his convoy or bystanders, according to wire service reports.

The renewed fighting Tuesday followed an especially bloody day for U.S. forces. On Monday, a car bomb exploded near a military convoy on the outskirts of Fallujah and killed seven U.S. Marines, the U.S. military reported. The attack, which also killed three Iraqi National Guardsmen, was the deadliest against U.S. troops in four months.

The American casualties were members of the 1st Marine Expeditionary Force, which is responsible for security in Anbar province, a stronghold for Sunni Muslim insurgents west of Baghdad. The names of the dead were withheld until their relatives could be notified.

The bomb detonated as the convoy traveled down a barren stretch of road nine miles from Fallujah, U.S. officials said. Two Humvees were reduced to smoldering wreckage, video footage from the Arab satellite channel al-Arabiya showed. U.S. forces removed the bodies and military helicopters flew in.

"This desperate act of inhumanity will only serve to strengthen our commitment to the Iraqi people," the U.S. military said in a statement. "Our forces will continue to stay the course in order to ensure Iraqi security forces have everything necessary to set the conditions required to foster rule of law and revitalization in Iraq."

Marine patrols have not entered Fallujah since the end of a three-week siege in April; the city has been under the control of insurgents. The U.S. military has targeted buildings in the city with periodic air strikes in an attempt to ferret out the insurgents. U.S. officials say they believe Jordanian guerrilla leader Abu Musab Zarqawi is using the city as his base of operations.

The killing of the seven American troops on Monday represented the highest toll in a single attack since April 29, when eight U.S. soldiers were killed in a car bombing in a southern suburb of Baghdad.

Meanwhile Monday, the Interior Ministry announced that authorities no longer believe that a man in Iraqi police custody is Izzat Ibrahim Douri, a top deputy to former president Saddam Hussein and one of the U.S. military's two most-wanted fugitives, along with Zarqawi. Ministry spokesman Sabah Kadhim said medical tests concluded that the man was a relative of Douri's. "We are investigating with him to reach the whereabouts" of Douri, Kadhim said.

Iraqi officials said on Sunday that they had captured Douri in a raid on a clinic near Tikrit, Hussein's home town. The report drew widespread coverage on Arab TV channels, as U.S. authorities cast doubt on the claim.

In a separate development Monday, kidnappers released a Turkish truck driver who had been held hostage. The release came after his two employers agreed to demands that they stop working in the country, according to al-Arabiya. The hostage, Midhit Civi, said in a video aired on the station that his captors had treated him well.

U.S.-led forces currently have 5,500 suspected insurgents in custody, Maj. Gen. Geoffrey Miller, deputy commander of detention operations in Iraq, said on Monday. Miller said interrogators were having increasing success picking up useful intelligence using new questioning procedures introduced at the two main U.S. detention facilities in Iraq following revelation of prisoner abuse by U.S. soldiers.

The military is holding 2,400 people at Abu Ghraib, the prison west of Baghdad where the abuses occurred, and 2,500 at Camp Bucca near the southern port city of Umm Qasr. Earlier this year, Abu Ghraib had close to 7,000 inmates.

Miller said the number of "high-value" reports -- information defined as "actionable intelligence" that could be used almost immediately in operations aimed at stopping insurgents -- had increased from about 200 in July to 325 in August.

Miller's characterization of intelligence gleaned from interrogations contradicted recent warnings voiced by senior military officials in Washington. The officials, including Maj. Gen. George R. Fay, who headed an Army probe of military intelligence soldiers involved in the abuse at Abu Ghraib, have said that the abuse scandal has had a chilling effect on military intelligence-gathering operations because interrogators are being more cautious and detainees have been tipped off to U.S. interrogation methods.

The new procedures are meant to yield useful information and end abuse. Among other new restrictions, interrogators are not allowed to keep prisoners in stress positions, according to U.S. officials. The new procedures also are aimed at improving cooperation between military intelligence and military police, as well as follow-up reviews of interrogations.

A nine-member board composed of six representatives from the Iraqi government and three officers from foreign military forces meets to decide whether there is sufficient evidence to hold detainees, Miller said. Previously, a three-member board consisting only of representatives of the foreign forces reviewed the cases.

The new board has reviewed the cases of 650 detainees since it began meeting Aug. 21, and of those, it has recommended 420 detainees for release, according to the U.S. military. "We think this is a significant step forward, as the Iraqis are making decisions about the returning of Iraqi citizens into society," Miller said.

In Baghdad on Monday, several hundred protesters marched peacefully through streets near the fortified area where the interim government and U.S. Embassy are headquartered. The crowd, consisting mostly of men, displayed banners, some of which read, "Yes for the law. No for the gun militia."

Iraqi police closed off portions of a commercial street to allow the protesters to pass without traffic. "We need to have a conference. We don't need to have weapons," one white banner read. The protesters were mostly former Iraqi army soldiers who say they want to return to their jobs.

Branigin reported from Washington.