A series of blasts struck the U.S.-protected Green Zone on Thursday, but the U.S. military said nobody was killed in the attack, which occurred on the American celebration of Thanksgiving.

About 10 blasts were heard in central Baghdad just before 5 p.m., and a huge plume of black smoke rose into the sky as the sun was setting. The U.S. government public address system in the Green Zone also warned people to "duck and cover" and to stay away from windows.

Maj. Brad Leighton confirmed the area was hit by indirect fire, a term the U.S. military uses for rocket or mortar attacks, but said nobody was killed. Some people were wounded, but they were not coalition forces, he said, declining to specify numbers or nationalities of those injured.

An Iraqi police officer, who spoke on condition of anonymity because he wasn't authorized to release the information, said the blasts were caused by mortars, but that could not be independently confirmed.

The heavily fortified area, which houses the U.S. Embassy and thousands of American troops and contractors, along with the Iraqi government's headquarters, has frequently been hit by rockets or mortars. But the attacks have tapered off amid a lull of violence in the capital and surrounding areas.

On July 10, extremists unleashed a barrage of more than a dozen mortars or rockets into the Green Zone, killing at least three people — including an American — and wounding 18.