A blast at a popular market in eastern Baghdad's Shi'ite Sadr City slum killed at least 10 people and wounded 65.
Another car bomb blew up next to a group of laborers queuing for work, killing six people and wounding 16.
Two other blasts shook a market area of Husseiniya, on Baghdad's northern outskirts, killing four, and a street in eastern Baghdad, apparently targeting the convoy of an Interior Ministry official, killing one of his guards and a bystander.
The explosion caused major damage to buildings and they even hurt some children, shopkeeper Abdul-Jabar Saad said of that attack, which he witnessed. God damn these people.
Hours after the four early explosions, south Baghdad's Um al-Maalif neighborhood was shaken by two separate blasts in the same market, killing 12 bystanders and wounding 25 others.
The latest spate of lethal attacks followed a week of arrests in Baghdad by Iraq's Shi'ite-led government of Sunni Arab fighters known as Awakening Councils, or Majalis al-Sahwa in Arabic.
Interior Ministry officials declined to comment on whether the bombs were a coordinated strike or a reaction to the arrests, one of which sparked clashes Saturday between Iraqi forces and supporters of their arrested Sahwa leader.
The government insists it is only detaining those wanted for grave crimes, but the fighters -- many of them former insurgents -- fear it is settling sectarian scores.
Analyst Kadhum al-Muqdadi, a professor at Baghdad University, said such a connection was not unlikely.
Any security action carries the risk of a reaction, he told Reuters. These could be the work of Sahwas or just of opportunists exploiting this issue.
The Sahwas first switched sides and joined with U.S. forces to battle Sunni Islamist al Qaeda in late 2006, manning checkpoints and conducting raids throughout the country.
The Iraqi government started taking control of their operations late last year, but mistrust between the two runs deep. Some of the guards complain they have not been paid for two months, although Iraqi officials say that was an administrative glitch that has now been fixed.
Iraqi and U.S. officials say a small number of the 90,000-odd Sunni guards have been infiltrated by al Qaeda and other insurgent groups.
Overall violence has fallen in Iraq to levels not seen since late 2003, but militants still carry out frequent, large-scale bomb attacks, especially in the capital and the northern provinces of Diyala and Nineveh.