The blast near a Shia mosque in al-Musayyib, near Karbala, also wounded 82 people and destroyed nine cars, police said on Saturday.
"This is a black day in the history of the town," al-Musayyib police chief Yas Khudayr said by telephone.
Some people who rushed to the scene discovered they had lost loved ones. "After the bomb, I went over there and found my son's head. I could not find his body," said Mohsen Jassim of his 18-year-old son.
Al-Qaida claimed responsibility for a bombing campaign in its second day and said more violence would follow.
"The Hassan Ibrahim al-Zaidi attack continues for the
second day in a row, with rigged cars, martyrdom attacks and clashes," said a purported al-Qaida statement on a website.
Bombers killed 32 people in
Iraq on Friday
There were no signs that al-Qaida's operatives had taken over any parts of the capital, but the frenzy of bombings was a bloody reminder that the government has a long way to go before stamping out such attacks.
Fighters struck elsewhere hours before the bombing at al-Musayyib, killing at least 16 people.
British soldiers killed
The strikes come a day after 10 bombers blew themselves up across Baghdad and an 11th attacked Iskindiriya, south of the capital. In all, they killed at least 32 people, police said.
In Amara in southeast Iraq, three British soldiers died in what the Ministry of Defence in London said was a suspected roadside bomb. A little-known Iraqi group said in a web statement that it was behind the killing.
"Thank God, this morning ... three British soldiers were killed and at least three others were injured by exploding a package by their patrol in the Maysan province," the group, calling itself the Imam Hussein Brigades, said.
The statement was posted on a site used by the main Iraqi insurgent groups, including the al-Qaida group led by Abu Musab al-Zarqawi. But unlike those mainly Sunni groups, the name suggested it was a Shia group. It said it also killed an
Iraqi judge in the town of Nassiriya.
Also on Saturday, at least eight Iraqis were killed after two bombers blew themselves up inside a mosque near al-Hilla city, south of Baghdad, while afternoon prayers were under way.
Twelve others were injured in the blast.
A spate of bombings have left
many killed and injured in Baghdad
The Ijbala Shia mosque and nearby houses were severely damaged in the attack, Iraqi journalist Walid Khalid told Aljazeera.
Elsewhere in Iraq, a car bomb targeting Iraqi police officers killed four Iraqis, including two children, a police officer and a civilian. Eleven others, including seven police officers, were wounded in the attack in Dora, in southern Baghdad.
In al-Mashada area, north of Baghdad, an armed group ambushed a 10-vehicle convoy of Interior Ministry police officers, known at al-Dhib Brigades. The police exchanged fire with the attackers.
An unknown number of police were killed and injured, reported Khalid.