Several people were seriously injured in the attack, which took place at a campaign rally for the Asa’ib Ahl al-Haq party.
The attack comes less than a weeks before Iraqis are due to head to the polls in parliamentary elections.
Iraq has been enduring the worst unrest since it pulled back from the brink of civil war in 2008.
Three bombs exploded as people left the rally, says the BBC’s Nahed Abouzeid in Baghdad.
The first two blasts were caused by truck bombs and the third by a roadside bomb.
Desperate act
Asa’ib Ahl al-Haq is backed by Iran and is a public supporter of Syrian President Bashar al-Assad.
This is likely to have antagonised Sunni groups in both countries, our correspondent says.
The rally had been addressed by cleric Sheik Qais al-Khazali, who told the crowd: “We are ready and prepared to defend this nation. Let it be known that Asaib will be the remedy.”
Next Wednesday’s election will be the first since the US pulled out combat troops in 2011.
More than 9,000 candidates will compete for 328 parliamentary seats, but there will be no voting in parts of Sunni-dominated Anbar province, where security forces still battle Islamist and tribal militants for control of the provincial capital Ramadi and nearby Fallujah.
Source: BBC News
