Authorities said most of the victims were Shiite Muslim pilgrims gathering to observe the anniversary of the death of one of their most revered religious figures, CNN reported.
Hundreds of thousands of Shiite pilgrims have begun walking to Kadhimya for the annual commemoration Saturday of the death of Imam Moussa al-Kadhim, grandson of the Prophet Mohammed. The shrine to al-Kadhim in Baghdad is one of Shiite Islam's holiest sites.
An Interior Ministry official said four parked cars detonated across Baghdad, aimed at Shiite pilgrims, The New York Times reported.
In the predominately Shiite city of Hilla, south of Baghdad, two car bombs killed at least 20 people and injured nearly 40 others, the Times said. The explosions hit two Shiite mosques and a restaurant.
Martin Kobler, the U.N. secretary-general's special representative for Iraq, said he was "deeply shocked and utterly dismayed by the despicable attacks."
"The scale of the violence is disturbing," Kobler said. "I urgently appeal to the government to address the root causes of the violence and terrorism that are causing so much suffering and pain to the Iraqi people."
Also, homemade bombs damaged Shiite mosques in the Hilla area, but no casualties were reported, the Times said.
In a village east of Karbala, officials said a bomb hit a group of laborers.