The rating decision by Fitch follows an August 5 downgrade of U.S. debt by rival Standard & Poor's that sparked a sharp drop in global stock markets.

　　In the meantime, a series of reports paint a mixed picture of the U.S. economy. Tuesday's data from the Commerce Department says the number of housing starts dropped 1.5 percent in July. If construction continued at the same pace for a full year, just 604,000 homes would be built. Experts say that is far below the level seen in a healthy housing market.

　　A separate report showed industrial production rose in July as carmakers started to recover from the supply disruptions caused by Japan's natural disasters. The U.S. central bank says production at factories, mines and utilities gained nine-tenths of a percent in July, which is a bigger gain than the previous month.

　　Still another report showed that the costs of goods imported to the United States rose three-tenths of a percent in July, in part due to increasing oil costs.

　　And U.S.-based Wal-Mart, the world's largest retailer, has not yet been able to boost sales in its home market. But Wal-Mart's international sales helped the store's overall profits grow by 5.7 percent in April, May, and June.