Baghdad, Iraq (CNN) -- A motorcycle bomb killed 20 people and injured 117 others south of Baghdad on Wednesday, the Interior Ministry said.
The bombing in the holy city of Karbala was one of four attacks targeting Shiite pilgrims as they headed toward the shrine of Imam Hussein on Wednesday morning, a ministry official said.
Three people died and 23 were injured in the other attacks.
In those explosions, a roadside bomb in western Baghdad killed one person, and a roadside bomb in the city of Hilla in Babil province, south of Baghdad, killed two people. A roadside bomb in southwestern Baghdad caused only injuries.
Wednesday's attacks came two days after a suicide bomber killed 41 people and wounded 106 others in an assault on pilgrims in northeastern Baghdad.
Iraqi authorities are trying to provide security to thousands of Shiite worshipers who are making their way to Karbala to mark the Arbaeen -- the end of the 40-day mourning period at the close of Ashura.
Ashura commemorates the martyrdom of Hussein, the grandson of the Prophet Mohammed who was killed in battle in Karbala in 680 A.D. That event helped create the schism between Sunnis and Shiites, the two main Muslim religious movements.
CNN's Yousif Bassil contributed to this report.