The Shiites responded almost immediately, firing 10 mortar rounds at the Abu Hanifa Sunni mosque in Azamiya, killing one person and wounding 14 people in an attack on the holiest Sunni shrine in Baghdad.
In the aftermath, the Iraqi government imposed a curfew in Baghdad for Thursday night. The Interior Ministry said the curfew would go into effect at 8 p.m. Thursday and that all people and vehicles must stay off the streets of the city until further notice.
Beginning at 3:10 p.m., the three car bomb attackers in Sadr City blew up their vehicles one after another, at 15 minute intervals, hitting Jamila market, al-Hay market and al-Shahidein Square. At about the same time, two mortar rounds struck al-Shahidein Square and Mudhaffar Square, police said.
Brig. Gen. Abdul-Karim Khalaf, a spokesman for the Interior Ministry, told state-run Iraqiyah television that other than the vehicles that exploded, one car was captured and three were still on the run. He gave the license plate numbers of each car, asking residents in Sadr City to inform police if they saw them.
As the three fiery explosions sent up huge plumes of black smoke up over northeastern Baghdad, and left streets covered with burning bodies and blood, angry residents and armed Shiite militiamen flooded the streets, hurling curses at Sunni Muslims and firing weapons into the air.
Sadr City is the home of the Mahdi Army, the militia loyal to radical anti-American Shiite cleric Muqtada al-Sadr.
Ambulances raced to burning wooden fruit and vegetables stalls in Jamila market to rescue dozens of wounded people. Rescue workers also removed burned bodies from mangled cars and minibuses and took them away on wheeled carts. But many other corpses of adults and children remained in the streets.
Shortly after the attack, Mahdi Army militiamen deployed around the area, setting up checkpoints and roadblocks in the area to keep all strangers away.
The coordinated attack was the deadliest in Iraq since the U.S.-led war began in March 2003.
It surpassed a bombing in the southern city of Hillah that targeted mostly Shiite police and National Guard recruits, killing 125 and wounding more than 140 in February 2004. On March 2, 2004, coordinated blasts from suicide bombers, mortars and planted explosives struck Shiite Muslim shrines in Karbala and Baghdad, killing a total of at least 181 Iraqis and wounding 573. But that attack occurred in two separate cities.
Police Col. Hassan Chaloub said at least 150 people were killed and 238 wounded in Thursday's attack.
In other developments:
Sectarian fighting also broke in another part of northern Iraq on Thursday, when 30 Sunni insurgents armed with machine guns and mortars attacked the Shiite-controlled Health Ministry building. After a three-hour battle, during which Iraqi soldiers and U.S. military helicopters intervened, the attackers were repulsed. But at least seven guards of the ministry were wounded, said police 1st. Lt. Maitham Abdul-Razaq.
The Sadr City and Health Ministry attacks were the latest example of widespread sectarian fighting involving Sunnis and Shiites that is leaving Iraq either on the verge of a civil war or already fighting one.
At about noon Thursday, heavy clashes broke out between about suspected Sunni insurgent gunmen and guards at the Shiite-controlled Health Ministry building in northwest Baghdad, security officials said.
State-run Iraqiyah television said the Health Ministry was being attacked with mortars by "terrorists who are intending to take control of the building."
Security officials said about 30 gunmen, believed to be Sunni insurgents, had launched the attack. Iraqi troops were being rushed to the area and all roads leading to the ministry in Bab al-Muadham neighborhood were closed, said the security officials on condition of anonymity because they were not authorized to speak to reporters.
Police Lt. Ali Muhsin said the attack began at 12:15 p.m. when three mortar shells hit the building, causing damage. After that, gunmen on the upper floors of surrounding buildings opened fire.
Ministry workers were trapped in the building.
"The gunmen fled as American helicopters and Iraqi armored vehicles arrived. Employees were able to leave starting about 3:15 p.m.," Health ministry spokesman Qassim Yehyah said.
Health Minister Ali al-Shemari is a follower of al-Sadr, the radical anti-American Shiite cleric.
Earlier Thursday, U.S. and Iraqi forces searching for a kidnapped American soldier also had swept through an area of Sadr City, killing four Iraqis, wounding eight and detaining five, police said.
The raid was the fourth in six days that coalition forces have raided Sadr City, which is home to the Mahdi Army, the militia loyal to radical anti-American Shiite cleric Muqtada al-Sadr.
The militia is suspected of having kidnapped U.S. soldier Ahmed Qusai al-Taayie, a 41-year-old Ann Arbor, Michigan, resident as he was was visiting his Iraqi wife in Baghdad on Oct. 23.
The Mahdi Army also is suspected of having kidnapped scores of people during the raid on a Ministry of Higher Education office in Baghdad on Nov. 14. The ministry is predominantly Sunni Arab.