Sunni Muslim insurgents and Shiite Muslim militiamen mounted attacks on U.S. soldiers across Baghdad on Monday night and Tuesday morning that raised the U.S. military's two-day death toll to 14 and illustrated the dangers that continue to confront American forces in the Iraqi capital.

Three soldiers were killed in separate assaults here Tuesday, the U.S. military command said. The military also reported that four soldiers were killed in different attacks Monday in or near Baghdad, in addition to the seven Marines killed in a car bomb attack near the restive city of Fallujah. A total of 998 uniformed U.S. service members and three civilian employees of the Defense Department have been killed since military operations began in Iraq in March 2003, according to Pentagon figures.

The most significant attack occurred in Baghdad's Sadr City slum, where militiamen loyal to Shiite cleric Moqtada Sadr ambushed U.S. Army patrols early Tuesday, sparking battles in which two U.S. soldiers and an estimated 33 Iraqis were killed, according to U.S. and Iraqi officials. The clashes shattered a nine-day lull in violence in the neighborhood and threw into doubt pledges by Sadr's aides that the cleric wants to renounce militancy and participate in the country's nascent political process.

Tuesday's violence in Baghdad was not restricted to the U.S. military. In the central part of the capital, gunmen barged into the offices of an Italian humanitarian aid organization and kidnapped two Italian women and two Iraqi staff members. Elsewhere in the city, a roadside bomb struck a motorcade ferrying Baghdad's governor, killing two people but leaving him uninjured, according to the Interior Ministry.

On Tuesday evening, U.S. Marine units pounded targets in Fallujah with tank rounds, artillery shells and bombs after Marines and Iraqi security forces operating just outside the city were fired on. The 1st Marine Expeditionary Force estimated that as many as 100 insurgents may have been killed in the counterattack, but the account could not be independently verified.

The fighting in Sadr City began shortly after midnight when Army patrols were hit with rocket-propelled grenades and roadside bombs, military officials said. Soldiers returned fire with small arms and large-caliber machine guns before summoning tanks, attack helicopters and fighter jets for additional firepower.

"We just kept coming under fire," said Army Capt. Brian O'Malley.

At 9:30 a.m., a group of soldiers waiting for an explosive-ordnance disposal team to defuse a roadside bomb was attacked with a rocket-propelled grenade. One soldier was killed and two others were wounded. Another soldier was killed at noon in a separate attack in the same area.

A spokesman for the Health Ministry said at least 33 Iraqis were killed and 145 were wounded in the clashes in Sadr City, which raged almost continuously for more than 12 hours, finally subsiding in the early afternoon.

As evening approached, Bradley Fighting Vehicles and other armored personnel carriers from the Army's 1st Cavalry Division occupied key intersections in the vast slum, which is home to about 2 million people. Militiamen, who had strutted around with rocket launchers and assault rifles in the morning, retreated into alleys and apartment buildings.

The violence was the first major battle between U.S. forces and Sadr's Mahdi 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 Iraq's most influential Shiite religious leader. A few days later, on Aug. 30, Sadr announced through aides that he was planning to participate in politics and ordered his militia to suspend attacks on U.S. and Iraqi forces.

But Tuesday's clashes dashed hopes among Iraqi and U.S. officials that Sadr would live up to those commitments. "It's not his promises but his actions that we have to focus on," said a senior Iraqi government official, speaking on condition of anonymity. "Up until now, we haven't seen any signs that they are serious about peace."

A senior U.S. official in Iraq said recent intelligence reports have shown that Mahdi Army militiamen in Sadr City have been reorganizing and rearming since the compromise in Najaf.

A top Sadr aide, Ali Yassiri, accused U.S. forces of sparking the fight by violating an informal cease-fire in Sadr City while Sadr's representatives tried to negotiate a peace deal with Iraq's interim government. Although the talks have not broken off, they remained stalled over Sadr's demands that his supporters be allowed to retain their weapons and that U.S. forces be barred from entering Sadr City, requests to which the government has been unwilling to accede.

"The occupation forces are trying to incite us," Yassiri said. "We received orders that the negotiations should continue, but the occupation forces are trying to make these negotiations fail and start another battle."

The kidnapping of the two Italians and two Iraqis was one of the boldest assaults on foreign civilians in the capital. Witnesses said as many as 20 men armed with AK-47 assault rifles and pistols stormed into the aid group's house, located near a busy commercial district, and hustled out their captives at gunpoint.

Officials with the organization Bridge to Baghdad, which has operated in Iraq since the 1991 Persian Gulf War, identified the women as Simona Torretta and Simona Pari, both 29. The women were involved in a project to boost school attendance in Sadr City and the southern port city of Basra, said Jean-Dominique Bunel, the director of a group that coordinates the work of nongovernmental organizations in Iraq.

Bunel said his group had been in contact with religious authorities for assistance in getting the hostages released, although it was not clear which of the many shadowy kidnapping outfits operating in Iraq carried out the abduction. "We will all work for their release," he said.

More than 100 foreigners and Iraqis have been kidnapped this year, but most of the abductions have taken place outside Baghdad. Two other Italians taken hostage have been killed by their captors: journalist Enzo Baldoni, who was captured last month as he traveled to Najaf, and security guard Fabrizio Quattrocchi, who was seized in April in western Iraq.

Italy has about 2,700 troops in Iraq, the third-largest contingent of soldiers in the country after those of the United States and Britain.

The other U.S. soldier killed Tuesday was hit with small-arms fire in western Baghdad. The soldier, with the 89th Military Police Brigade, was guarding a convoy of fuel tankers that had been attacked by insurgents a few hours earlier when he was shot by a sniper atop a nearby school, witnesses said.

Three of the four soldiers killed in or near Baghdad on Monday were attacked with roadside bombs, the military said. The cause of death of the fourth soldier was not released.

Correspondent Daniel Williams in Rome and special correspondents Luma Mousawi, Khalid Saffar and Bassam Sebti in Baghdad contributed to this report.

A militant aims a grenade launcher in Baghdad's Sadr City slum, where two U.S. soldiers were killed Tuesday.Backers of Moqtada Sadr look for U.S. soldiers in Sadr City. An ambush on U.S. Army patrols early Tuesday set off hours of fighting in the Baghdad slum.