Nearly 10 blasts were heard in the sprawling area in central Baghdad starting about 6:15 a.m., and the U.S. public address system there warned people to "duck and cover" and to stay away from windows.

Maj. Brad Leighton, a U.S. military spokesman, confirmed the Green Zone was hit by indirect fire, the military's term for a rocket or mortar attack, but could not immediately provide more details.