US aircraft have joined Iraqi military ground forces in their effort to crack down on Shi'ite militias.
Coalition jets carried out air strikes Friday in the southern oil city of Basra, where Iraqi troops have been battling militants since Tuesday.
In Baghdad, US helicopters fired on insurgents in the Sadr City neighborhood.
Iraqi President Nuri al-Malaki has vowed to continue the attack against the militias, and on Friday he extended until April 8th a deadline for militant fighters to surrender their weapons.
In Washington, President Bush said the upsurge in violence in southern Iraq and parts of Baghdad represents a "defining moment" in the history of a free Iraq.
Mr. Bush said efforts by Iraqi forces to subdue Shi'ite militias are going to take a while, but are a necessary part of the development of a free society. He said Iraq's government must be willing to confront those criminal elements.
Separately, two Iraqi guards were killed Friday outside the office of Vice President Tareq al-Hashemi. Two rounds fired by insurgents hit the building.
Militants have been bombarding the Green Zone since Sunday. At least two Americans have been killed in the attacks, and the US State Department has urged all US Embassy personnel to stay inside reinforced buildings.
The US military also has reported the death of a US soldier who was mortally wounded by a roadside bomb blast south of Baghdad on Friday.