The bus station bombing occurred about 200 yards from the Imam Hussein shrine in Karbala, where the grandson of Islam's Prophet Muhammad is buried — one of the most important sites for Shiites. After the attack, hundreds of people swarmed around ambulances, crying out and pounding their chests, and attacking police who tried to clear the roadway.

"I want my father. Where is my father?" 11-year-old Sajad Kadhim cried out as he lay on the grounds of the hospital, where doctors were treating his burns.

"All I remember was we were shopping. My father was holding my hand and suddenly there was a big explosion. I don't know where my father is. I want my father," the boy cried.

Dr. Khalid Adnan Obeid, director of Al-Hussein Hospital; Ghalib al-Daamai of the provincial security committee; and Rahman Mishawi, spokesman for Karbala police, all said 37 civilians were killed and 168 wounded. Earlier, hospital officials said at least 56 people had been killed.

State television aired footage from the scene, in which rescue workers could be seen evacuating casualties. The charred body of a child laid motionless on a stretcher.

At least 16 children were among the dead, said Brig. Gen. Abdul-Karim Khalaf, spokesman for the Interior Ministry. Iranian and Pakistani pilgrims were also among the casualties, said an official at Al-Hussein Hospital, on condition of anonymity because he was not authorized to release the information.

A 72-year-old woman who called herself Um Hussein ran through the hospital corridors looking for her daughter and 6-year-old grandson.

"They were near the bomb. They went to buy something for our lunch," she said, pounding her head in grief.

"What did they do to deserve this? To whom should I complain? There is no government to protect us," she moaned.

Rioters surrounded the Karbala governor's office and demanded his and provincial council members' resignations, blaming them for lax security. Mobs threw stones at the governor's office and set fire to the building.

"This bombing shows a security breach, and we are investigating where the shortcoming was," Khalaf said.

A curfew was imposed in the area, and the city's entrances were sealed off while police and soldiers patrolled the streets.

More than 168 people were wounded in the attack, said Dr. Saleem Kadhim, spokesman for Karbala health department.

Karbala, 50 miles south of Baghdad, is the destination of an annual Shiite pilgrimage. Hundreds of Shiite faithful were killed traveling back and forth to the city during this year's pilgrimage, which took place last month.

Separately, a suicide car bomb killed 10 people on a major bridge in downtown Baghdad — the second attack on a span over the Tigris river this week, police said. The Jadriyah bridge suffered little damage.

On Thursday, a suicide truck bomb completely collapsed the al-Sarafiyah bridge in northern Baghdad, killing 11 people and sending cars plummeting into the waters below.

Police said four would-be suicide attackers were killed today in the northern city of Kirkuk when one of them detonated his explosives belt prematurely. All four men were killed but no civilians were hurt, said police Brig. Adil Zain-Alabideen.

Also today, gunmen attacked the western Baghdad house of Adnan al-Dulaimi, head of the largest Sunni bloc in Iraq's parliament, police said. Al-Dulaimi was not at home at the time of the attack, and is believed to be in Jordan.

Clashes erupted between his guards and the gunmen, lasting about half an hour. Five guards were wounded, police said.

Three bodyguards of the deputy minister of industry, Mohammed Abdul Jabar, were injured in a drive-by shooting on his convoy in western Baghdad, police said. The minister was in the convoy but escaped injury.

In other violence, three civilians and a policeman were killed in drive-by shootings in Fallujah and Hillah, about 60 miles south of Baghdad, police said. Two policemen and a civilian died in a roadside bombing south of Baghdad, and another civilian died in a similar bombing in central Baghdad, police said.

A bomb planted in a garbage can missed a passing police patrol in Baghdad's southwestern Baya district today but injured three electricity workers who were working nearby, police said.

The U.S. military issued a statement saying American troops captured 17 suspected insurgents, including an alleged al-Qaida in Iraq member, during raids this morning.