While attention was focused on those attacks, police in Samarra said a suicide bomber sitting in a wheelchair talked his way into the city's operations center and detonated, killing the deputy commander.
The attacker on Sunday went after travelers enjoying tea and refreshments in a tent near Iskandariyah, 50 kilometers (30 miles) south of Baghdad, as authorities have fortified the capital and Karbala to try to keep away extremists.
The blast killed at least 56 people and injured 68, according to police and Dr. Mahmoud Abdul-Rida, director of the Babil health department, making it one of the worst this year.
Hours earlier, extremists attacked another group with guns and grenades in the predominantly Sunni Baghdad neighborhood of Dora, killing three and wounding 36, police said.
The roadside bombing Monday on the outskirts of Baghdad also wounded 15 people, police said.
An apparently coordinated attack occurred a few hours later when a roadside bomb went off in eastern Baghdad, injuring three civilians. A second bomb about 70 meters (yards) away went off a few minutes later, wounding a traffic policeman who was riding to the scene on his motorcycle.
Police officials, who spoke on condition of anonymity because they weren't authorized to release the information, described both of Monday's attacks.
The attack in Samarra killed Abdul Jabbar Rabeia, according to police and witnesses who also spoke on condition of anonymity because they were not allowed to release the information.
The witnesses said the bomber appeared to be physically impaired and not just using the wheelchair as a ruse.
He approached the main checkpoint to the operation room command and said he needed to see the commander to ask for help, and was pushed through. But he was referred to the deputy commander instead after he said he was unable to walk up the stairs to see the commander, who was on the second floor, according to police at the scene.
Samarra, 60 miles north of Baghdad, is the site of the golden domed Askariya mosque -- a Shiite shrine that was bombed two years ago, sparking waves of sectarian violence.
Gunmen also opened fire on a police convoy in the northwestern city of Mosul, which the U.S. military has said is the last urban stronghold of al-Qaida in Iraq. Four officers were killed in the attack, police said.
Karbala is the burial site of Imam Hussein, one of Shiite Islam's most revered figures, where ceremonies will culminate Wednesday to commemorate the end of the 40-day mourning period following the anniversary of his death.
Major Shiite events have frequently been targeted in the past by suspected Sunni insurgents led by al-Qaida in Iraq in their drive to stoke sectarian violence. The attacks have prompted U.S. and Iraqi forces to increase the number of checkpoints, and impose car bans and other measures in major Shiite cities to protect the worshippers.
Recent commemorations -- including the Ashoura festival in mid-January to mark Imam Hussein's death -- have passed without major bloodshed amid an overall decline in violence across Iraq.
But two days of attacks have exposed the vulnerability of the pilgrims who walk for days to reach the shrine of Hussein, the grandson of the Prophet Muhammad who died in a seventh century battle near Karbala.
Iraqi police and U.S. troops at a nearby base away quickly responded to blast at the rest stop, the military said. About 42,000 pilgrims had previously traveled through the same area without incident, the military added.
U.S. Col. Tom James, commander of the 4th Brigade, 3rd Infantry Division, which is responsible for the area, said Iraqi security forces had established extensive security along the pilgrimage routes as well as a cordon around Karbala.
"Unfortunately, just based on the complexity of these routes and the number of pilgrims it's difficult to completely secure them," he said in a telephone interview. "In this case, we think there was an attack from one of the flanks of these routes."
Suicide attacks and car bombings are frequently blamed on al-Qaida in Iraq, but James said it was too early to say who was behind Sunday's bombing, pending the investigation.
Iskandariyah was one of the main cities in an area dubbed "the triangle of death" for much of the U.S.-led war that began in March 2003. But it and other former insurgent strongholds have seen a steep drop in attacks in recent months that the U.S. military attributes to a Sunni revolt against al-Qaida in Iraq and an influx of American troops.
Sunni leaders denounced the bombing. Hard-line politician Adnan al-Dulaimi's bloc blamed the attack on foreigners "aiming to create sectarian strife and to destabilize the country."
