A rocket or mortar slammed into Baghdad's guarded Green Zone Sunday, the U.S. military said.

Sirens wailed and the public address system warned people to "duck and cover" and stay away from windows shortly before the blast.

The military said the Green Zone was hit by indirect fire, a term referring to rocket or mortar fire. But it provided no information about casualties.

Sunday's attack comes just over two weeks after an American was killed when a rocket struck the sprawling area that houses the U.S. Embassy and much of the Iraqi government.

The Iraqis assumed control of the Green Zone from the Americans on Jan. 1 under a new security agreement and have begun removing some of the protective blast falls around the area.