U.S. stocks extended losses on Thursday, with the major indexes falling 1 percent on worries the credit crisis in Greece could spread and disappointing chain store sales data for April.

The Dow Jones industrial average <.DJI> dropped 98.78 points, or 0.91 percent, to 10,769.34. The Standard & Poor's 500 Index <.SPX> fell 12.51 points, or 1.07 percent, to 1,153.39. The Nasdaq Composite Index <.IXIC> lost 29.08 points, or 1.21 percent, to 2,373.21.

(Reporting by Chuck Mikolajczak; Editing by Kenneth Barry)