Insurgents struck the Iraqi capital Wednesday with at least a dozen attacks that targeted Shiite Muslim civilians, Iraqi security forces and American troops, killing more than 160 people in the deadliest day of violence in Baghdad since the U.S. invasion more than two years ago.

U.S. military officials said the day-long wave of suicide bombings, rocket attacks and shootings across the city bore the hallmarks of al Qaeda in Iraq, the radical Sunni Muslim insurgent organization led by Abu Musab Zarqawi, a Jordanian.

The group did not immediately assert direct responsibility for the attacks, but an Internet statement issued in its name welcomed the start of "revenge battles throughout the land of Mesopotamia."

The statement linked the attacks to a U.S. and Iraqi offensive underway against insurgents in the northwestern city of Tall Afar. A subsequent audio recording attributed to Zarqawi, which was posted on the Internet, accused the Shiite-led Iraqi government of having declared war on Sunnis in that city. As a result, al Qaeda in Iraq "has decided to launch a comprehensive war on the Shiites all over Iraq, wherever and whenever they are found. This is revenge. . . . Take care, because we are not going to have mercy on you," the recording said, according to a translation by the Washington-based SITE Institute, a group that monitors radical Web sites.

The attacks appeared calculated to undermine public faith in the ability of the fledgling government to protect its people, by showing that insurgents could strike in Baghdad despite the U.S. and Iraqi military efforts to stop them. Some of Wednesday's attacks were carried out in ways that maximized death tolls.

In northwest Baghdad, a driver in the heavily Shiite neighborhood of Kadhimiyah pulled up alongside a gathering point for day laborers and offered the men jobs, witnesses said. He waited until a crowd of workers had clustered around his four-door car, then detonated explosives packed inside, said Salim Hussein, 20, who witnessed the attack.

The blast killed at least 112 people and wounded hundreds of others.

As burned, blackened victims filled the district hospital, a Shiite cleric patrolled the scene of the bombing in an ambulance, calling over the vehicle's loudspeaker for donations of blood. Men looking for loved ones ran fingers down pages and pages of names of bombing victims posted outside the hospital.

"Why haven't they killed Saddam?" wailed a Shiite woman in black abaya as she walked away from the hospital. "Cut his head off."

Within an hour of that attack, a driver smashed his car into two other vehicles at an intersection, then blew up the vehicle when a crowd gathered, police said. At least 15 people died, police Lt. Mustafa Majid said.

"I saw people's bodies flying in the air and thrown for yards," minibus-taxi driver Amer Salman said.

More attacks were mounted throughout the day, signaled by rattling booms, black smoke and U.S. military helicopters shuttling across the sky. Traffic on main roads shut down as police closed key routes. Rumors spread that more car bombers were roaming the city and that men wearing suicide belts were infiltrating hospitals.

The other attacks included two car bombings that killed a total of 26 people, one that targeted an Iraqi army convoy and killed three soldiers, and two that hit U.S. military convoys, U.S. and Iraqi officials said. A U.S. military spokesman, Lt. Col. Steve Boylan, said that he knew of three U.S. soldiers wounded in the day's attacks and that none had been reported killed.

Separately, attackers opened fire on a car carrying Iraqi police officers, killing one, and then detonated a car bomb when other officers responded, killing four more people, police said. A separate rocket attack killed two Iraqi civilians.

In Taji, a town just north of Baghdad, men wearing the uniforms of Iraqi security forces dragged 17 men out of their homes, then handcuffed, blindfolded and shot them, news agencies reported.

A U.S. military convoy came under intense attack in the late afternoon, first with a roadside bomb and then, half an hour later, with a car bomb, police said. A reporter watched as U.S. forces traded gunfire with hidden assailants at the scene.

One of the final bombings of the day hit outside the Green Zone, the concrete- and razor-wire barricaded base of U.S. officials and the Iraqi government. There was no immediate official word on casualties.

The estimated death toll of more than 160 made Wednesday the deadliest day of insurgent violence in Baghdad since the United States and its allies invaded Iraq in March 2003. The deadliest day of insurgent violence nationwide was March 2, 2004, when at least 181 people were killed in mortar and bomb attacks on Shiite shrines in Karbala and Baghdad.

The violence continued Thursday morning when a car bomb exploded in Baghdad's southern Dora neighborhood. An Iraqi official said five Interior Ministry commandos were killed in the blast. The Associated Press reported that 21 people were killed -- 16 policemen and five civilians -- and that 21 others were wounded.

Prime Minister Ibrahim Jafari, who was visiting Dearborn, Mich., as part of a U.S. tour, condemned Wednesday's attacks and declared that his government's "rational, political struggle" would prevail over "criminal acts," the AP reported. "I share with the people their sorrow and grief. They are martyrs," Jafari said.

Survivors condemned the insurgents but blamed their government as well. "We voted for Jafari so he can help us get rid of terrorism. He cannot," Hussein Lami, a laborer, said at the site of the first bombing. "He must admit now that he cannot do it" and resign.

"Every day I am losing one of my friends or my relatives," Lami said.

Wednesday's carnage tested the ability of U.S. and Iraqi forces to maintain security shortly before two events that insurgents are widely expected to target: a Shiite pilgrimage this week that is expected to draw millions to the holy city of Karbala, and an Oct. 15 national referendum on Iraq's draft constitution. While voter registration among Sunnis has soared ahead of the vote, Zarqawi has declared that anyone who goes near a polling place is a legitimate target.

Growing political violence in much of the country also threatens what U.S. officials have said is their goal of bringing the insurgency to a level that is manageable by Iraqi forces ahead of any U.S. withdrawal.

Special correspondent Bassam Sebti contributed to this report.

Iraqis outside a Baghdad hospital grieve over the bodies of job-seekers killed in the deadliest attack of the day, a suicide car bombing in which 112 died.Iraqi personnel respond to the site of a massive bombing in Baghdad. The dozen attacks made Wednesday the deadliest in the capital since the 2003 invasion.A man faints after learning that seven of his relatives were injured in a massive car bomb attack while seeking day jobs in a Baghdad neighborhood.