Car and roadside bombs in Baghdad and predominantly Shi'ite provinces of Iraq killed at least 21 people on Sunday, police sources said.
No group immediately claimed responsibility of Sunday's the attacks, which appeared coordinated, but Sunni Islamist insurgents, including an al Qaeda affiliate, have been regaining momentum in recent months.
More than two years of civil war in neighboring Syria have aggravated deep-rooted sectarian divisions in Iraq, fraying an uneasy government coalition of Shi'ite, Sunni and ethnic Kurdish factions.
The deadliest attacks were in the city of Hilla, where two parked car bombs exploded simultaneously near a busy market and a third blew up near a vehicle repair workshop killing nine people in total, police said.
"I was about to get my breakfast in a nearby restaurant when a huge explosion happened and smoke and dust filled the place. Before I had taken a step forward another explosion happened," witness Abu Ahmed, who runs a grocery store, said.
"I ran to check on my son who was covering for me in my shop and found him covered with blood among many other bodies. There is no trace left of my shop."
Another explosion took place in the oil-exporting southern city of Basra, where a car bomb blew up near another vehicle repair workshop killing five people, and another car bomb in the city of Kerbala killed two others, police said.
In the capital, three security personnel were killed when a car bomb exploded near the convoy of the deputy head of Baghdad provincial council, and two more were killed in a roadside bomb blast near a commercial street in a western district.
About 800 Iraqis were killed in August, according to the United Nations, with more than a third of the deadly attacks happening in Baghdad.
The bloodshed, 18 months after U.S. troops withdrew from Iraq, has stirred concerns about a return to the sectarian slaughter of 2006-7, when the monthly death toll sometimes topped 3,000.