The blast happened near a gathering of workers in Tayaran Square, about a kilometer (mile) from a sit-in held by supporters of influential Shiite cleric Moqtada al-Sadr to demand political reforms.
No organization claimed the attack but all suicide bombings carried out so far this year in the country have been claimed by Daesh (ISIL), the militant group that controls parts of northern and western Iraq, Reuters reported.
Earlier this month, UN Assistance Mission for Iraq (UNAMI) said a total of 670 Iraqis lost their lives the previous month, while 1,290 others were injured.
The UN mission added that the number of the civilians killed stood at 410, and the number of civilians injured was 1,050. Violence claimed the lives of 260 members of the Iraqi security forces while 240 others sustained injuries.