BAGHDAD, Iraq (AP) _ A large explosion shook central Baghdad on Friday, and smoke was seen rising from near the Sheraton Hotel beside Firdos Square.

The cause of the explosion was not immediately known. No damage was visible on the Sheraton, one of two neighboring hotels were many foreigners are staying surrounded by U.S. soldiers.

U.S. troops warned earlier in the day that followers of radical Shiite cleric Muqtada al-Sadr were planning possible bomb attacks near Firdos Square. Troops had imposed a curfew in the area.