The location of the operation was not identified but US commanders say Al-Qaeda fighters have shifted to northern Iraq, especially Diyala and Nineveh provinces, after being chased out of Baghdad by a "surge" of US troops.

"(Phantom Phoenix) is a series of joint Iraqi and coalition operations to pursue and neutralize remaining Al-Qaeda in Iraq and other extremist elements," Lieutenant General Ray Odierno, the number two commander of US forces in Iraq, said in a statement.

He added that the operation "will exploit recent security gains and disrupt terrorist support zones and enemy command and control."

One of the operations, dubbed Iron Harvest, involves four US infantry companies -- about 640 soldiers -- around the town of Muqdadiyah, 100 kilometres northeast of Baghdad in Diyala province, Colonel Brad Coffey told reporters in the provincial capital Baquba.