Investigation ordered after British-Iraqi raid on intelligence agency in Basra.
Armed men also launched attacks in and around Baghdad while a car bomb in the southern Baghdad district of Doura killed 12, police said.
US soldiers killed
Earlier on Tuesday, US officials announced that nine American soldiers were killed and four wounded in two separate attacks in northern and north-eastern Iraq.
“Six Task Force Lightning soldiers were attacked while conducting combat operations in Salah ad Din province on March 5,” a statement said on Tuesday.
“The soldiers died as a result of injuries sustained following an explosion near their vehicles.”
In a second incident on the same day, three American soldiers were killed by a roadside bomb in Diyala, one other was wounded.
Iraqi and US forces are in the third week of a security crackdown in Baghdad aimed at stemming sectarian violence.
US military commanders had expressed concerns that fighters could step up attacks outside Baghdad while the operation was under way in the capital.
Also on Tuesday, fighters believed to have links to al-Qaeda stormed a prison in the northern city of Mosul, freeing up to 140 prisoners, but most were recaptured soon afterward, police said.
Officials said up to 300 fighters led by Abu Omar al-Baghdadi, leader of the Islamic State in Iraq, attacked Mosul‘s northwestern Badoush prison just after sunset.
Local police were overwhelmed by the fighters and had to call for back-up from US forces, officials said.
Hisham al-Hamdani, a member of the Mosul provincial government, said al-Baghdadi took part in the attack personally.
The Islamic State in Iraq is a body set up by al Qaeda’s Iraq wing and other Sunni fighter groups in October.
The prison has a poor security record, last December a nephew of Saddam Hussein, serving a life sentence for financing fighters, escaped with the help of a police officer.
Ayman Sabaawi remains at large.