Thousands of U.S. and Iraqi troops remained poised around the insurgent strongholds of Ramadi and Fallujah Saturday, as militants mounted a series of deadly attacks in the city of Samarra.

Authorities say at least 33 people, many of them policemen, were killed in four car bombings and attacks on police stations in Samarra, which lies within the so-called "Sunni Triangle."

Meanwhile, in Ramadi, another Sunni Triangle hotspot, at least 20 American Marines were wounded in an attack on their convoy.

In Fallujah, the heart of the insurgency, U.S. warplanes continued to bombard suspected militant targets ahead of what is expected to be a full scale military assault to crush rebels in the city.

And in Baghdad, the U.S. military says three soldiers were wounded and an Iraqi civilian killed in a car bomb explosion.