Police throughout Iraq look for clues after multiple car bombings kill or injure dozens.

In Basra, police say two car bombs exploded simultaneously, wounding at least 17.

One local shop owner saw both blasts go off.

(SOUNDBITE) (Arabic) OWNER OF SHOP AT BLAST SCENE, KADHIM FALEH, SAYING:

"A blast took place here and one minute later a second car bomb went off here. A man was wounded here [points] and another one there and a third one was lying under tires."

The attack was part of a wave of car bomb attacks that ripped through busy streets and markets in mostly Shi'ite provinces.

The deadliest attack took place in Hilla, south of Baghdad, where two more car bombs blew up in quick succession, killing at least five people and injuring many more.

It is not immediately clear who is behind the attacks, which appear to have been coordinated.

Sunni Islamists and other insurgents, including al-Qaeda, have been regaining ground this year.

So