The bloodshed - in four cities as far north as Mosul and as far west as Ramadi - struck directly at U.S. claims that the Sunni insurgency is waning and being replaced by Shiite militia violence as a major threat.
The deadliest blasts took place in Baqouba and Ramadi, two cities where the U.S. military has claimed varying degrees of success in getting Sunnis to turn against al Qaeda.
In Baqouba, the Diyala provincial capital 35 miles northeast of the capital, a parked car exploded about 11:30 a.m. in front of a restaurant across the street from the central courthouse and other government offices.
Many of the victims were on their way to the court, at the restaurant or in cars passing through the area. A man identifying himself as Abu Sarmad had just ordered lunch.
"I heard a big explosion and hot wind threw me from my chair to outside the restaurant," he said from his hospital bed.
The force of the blast jolted the concrete barriers erected along the road to protect the courthouse, witnesses said.
At least 40 people were killed and 70 wounded, according to hospital officials, who spoke on condition of anonymity because they weren't authorized to release the information.
The U.S. military in northern Iraq gave a slightly lower toll, saying 35 Iraqi citizens were killed, including a policeman, and 66 wounded. It said the blast destroyed three buses and damaged 10 shops.
AP Television News footage showed many of the bodies covered in crisp white sheets and black plastic bags in a hospital courtyard while the emergency room inside was overwhelmed with the wounded.
It was the deadliest bombing in Iraq since March 6, when a twin bombing killed 68 people in a crowded shopping district in the central Baghdad district of Karradah. The attack was also the deadliest in Baqouba since The Associated Press began tracking Iraqi casualties in late April 2005.
The U.S. military said Tuesday that attacks in Baqouba have dropped noticeably since last June. But a series of assassinations and other high-profile attacks have occurred in and around the city this year, and American commanders have consistently warned that al Qaeda-led insurgents continue to pose a serious danger.
"Although attacks such as today's event are tragic, it is not indicative of the overall security situation in Baqouba," Maj. Mike Garcia, a spokesman for U.S. forces in Diyala province, said in a statement.
According to an AP count, at least 126 Iraqis have been killed in war-related violence in Baqouba so far in 2008; the majority, 65, were killed in 10 separate bombings. At least 818 Iraqis were killed in war-related violence in the city last year, up slightly from 793 the year before.
Baqouba and Ramadi were strongholds of al Qaeda in Iraq and saw some of the fiercest fighting of the U.S.-led war until local Sunni tribal leaders fed up with the terror network's brutal tactics joined forces with the U.S. military against it last year.
The Sunni revolt, an influx of some 30,000 American troops and a cease-fire by radical Shiite cleric Muqtada al-Sadr led to a decline in violence there as well as in Baghdad.
In particular, the U.S. military has touted Ramadi as a success story. The former al Qaeda stronghold, 70 miles west of Baghdad, is the capital of Anbar province and has largely been sealed off by checkpoints.
Tuesday's bombing in Ramadi came about an hour after the Baqouba attack.
A suicide attacker on a motorcycle drove up to a kebab restaurant, went inside and detonated his explosives vest, killing at least 13 people, including three off-duty policemen and two children, and wounding 20, according to police and hospital officials.
Ahmed al-Dulaimi, a 27-year-old mechanic, escaped injury because he was sitting at a back table. But he said his cousin, who owned the restaurant, was killed.
"Suddenly a motorcycle parked near the restaurant and a man came running in and then a huge explosion took place," al-Dulaimi said. "Pieces of flesh flew into the air and the roof fell over us."
The blast in central Baghdad also took place shortly after midday. A parked car bomb targeted a police patrol, killing four civilians who were passing by and wounding 15 other people, police said.
The U.S. military condemned the bombings in Baqouba, Ramadi and Baghdad and said they appeared to have been carried out by al Qaeda in Iraq.
The fourth bombing took place in Mosul, a city 225 miles northwest of Baghdad that the U.S. military has called the last urban stronghold for al Qaeda in Iraq.
At 3:45 p.m., a double car bombing wounded three Iraqi policemen and 15 civilians, the U.S. military said. Iraqi police Brig. Gen. Khalid Abdul-Satter said the attack killed one civilian was killed and wounded 16 others.
U.S.-allied Sunni fighters have found themselves increasingly targeted by violence and frustrated by a perceived lack of support by the Shiite-dominated government.
The purported leader of the al Qaeda umbrella group, the Islamic State of Iraq, called on those who switched sides to return to the insurgency. He made his statement in an Internet audiotape posted Tuesday on a militant Web site.
Abu Omar al-Baghdadi, whom the U.S. has described as a fictitious character used to give an Iraqi face to the organization, urged the Sunnis to direct their arms against "the Crusaders and those who support them," using typical militant rhetoric for the United States.
While the Sunni insurgency has recently appeared to wane, the U.S. military has increasingly pointed to Shiite militia violence as one of the greatest threats to Iraq's stability.
On Tuesday, Shiite extremists clashed again with U.S.-Iraqi forces in Baghdad and the oil-rich southern city of Basra.
U.S. soldiers backed by an airstrike killed six militants after a gunbattle broke out in the Sudayrah area, near Baghdad's main Shiite militia stronghold of Sadr City, the military said. Iraqi police in the area claimed that two boys were among those killed in the airstrike, but the military said no civilian casualties were reported.
In southern Iraq, three aides to Iraq's top Shiite cleric, Grand Ayatollah Ali al-Sistani, escaped assassination in separate attacks Tuesday, although two of them were seriously wounded, police said.
The attacks came four days after a top al-Sadr aide was assassinated in Najaf.
In other developments:
- The State Department is they may be forced to serve in Iraq next year and says it will soon start identifying prime candidates for jobs at the Baghdad embassy and outlying provinces.
- The purported leader of al Qaeda's affiliate in Iraq called in a new Internet audiotape Tuesday on Sunni fighters who switched sides and joined the American push to pacify Sunni areas of the country, to return to the insurgency. In the recording, Abu Omar al-Baghdadi, who allegedly heads the Islamic State of Iraq, called on Sunni unity and urged Sunnis in the Iraqi army, police and the so-called "Awakening Councils" to abandon fighting the mujahideen, and instead turn their guns toward the "Crusader" enemy - shorthand for U.S. troops in Iraq.
- In northern Iraq, meanwhile, a parked car bomb exploded near an Iraqi army convoy west of Mosul, killing 12 Kurdish soldiers and wounding five, police chief Col. Mutlaq al-Shimmari said.
- In Tal Afar, south of Mosul, a suicide bomber attacked a funeral for a Shiite family, killing five people and wounding 22, Mayor Najim Abdullah said.