A car bomb explosion has killed at least 21 people and wounded 75 in Iraq's predominantly Shia southern city of Hilla.
A suicide bomber rammed his car into the entrance of a police headquarters in Hilla, 100km south of Baghdad, during a shift change when many police officers were outside the building.
The blast left a two-metre wide crater and badly damaged the police station.
'The suicide bomber took advantage of the police station's guards changing shifts to attack,' said Haidar al-Zazour, the head of the Babil provincial council security committee.
'He managed to drive through the main gate and blew up his vehicle four metres inside the station's perimeter.'
Iraqi security forces went on high alert for revenge attacks after US special forces killed al-Qaeda leader Osama bin Laden in Pakistan.
Iraq has been a major battlefield for the Islamist militant group since the 2003 US-led invasion that toppled Sunni dictator Saddam Hussein.
US and Iraqi officials say al-Qaeda in Iraq has been severely damaged in recent years.
