The attack, which happened overnight, came as Iraqis took to the streets for a fifth consecutive day, protesting their government's corruption, lack of services and other grievances.
Fourteen people were killed and 865 wounded, according to Al Jazeera, citing security sources.
"Iraqis' main demands are to address the issue of corruption, to step down, and for a new election to be held," Ali al-Nashmi, an Iraqi academic, told the news network.
The protests are similar to those that have engulfed Lebanon in recent days in that they are economically driven, largely leaderless and spontaneous against a sectarian-based system and a corrupt political class that has ruled for decades and driven the two countries to the brink of economic disaster.
At least 72 protesters -- not including the latest fatalities in Karbala -- have been killed since anti-government protests resumed across Iraq on Friday, after 149 were killed during an earlier wave of protests this month.
The Associated Press contributed to this report