(CNN) -- At least 21 people died when a suicide car bomb attack ripped through a police headquarters, a strike one official thinks is retaliation for Osama bin Laden's killing.
The incident occurred in the Babil province capital of Hilla, 100 kilometers or 62 miles south of Baghdad.
At least 75 people also were wounded in the attack, which occurred during a handover between the overnight and morning shifts, the Interior Ministry said.
The attack bears the hallmark of al Qaeda in Iraq, and Kadhim Majeed Toman, chairman of the Babil provincial council said, "I believe today's attack was revenge from al Qaeda after the killing of bin Laden in Pakistan."
The car bomb carried 150 kilograms of explosives, ministry officials said.
Attackers struck other targets as well in Iraq.
Police officials in the northern city of Kirkuk told CNN that two Kurdish security forces were killed and four others were wounded when a roadside bomb exploded at their patrol in the town of Tuz Khurmato.
In central Baghdad, one civilian was killed and four others were wounded when a roadside bomb exploded in the Nidhal commercial street. In eastern Baghdad, Gen. Moaed Khaleel, an army officer with Iraq's Defense Ministry was assassinated by gunmen.
Iraqi security forces have been on high alert in Baghdad and a number of provinces, including Diyala, Nineveh and Anbar, after bin Laden's killing in Pakistan on Monday. Al Qaeda is a largely Sunni Muslim group, and those areas have signficiant Sunni populations.
U.S. military spokesman Maj. Gen. Jeffrey Buchanan said bin Laden's death has generated some peace and closure but that it doesn't negate the challenges posed by al Qaeda in Iraq.
"We have been at this for a long time and we have a lot of work to do still," he said.
Overall, violence is down considerably in Iraq from its peak between 2005 and 2007. Yet assassinations, bombs, gunfire and mortar attacks remain regular occurrences.