Egan-Jones Ratings Co. cut the U.S. credit rating one step to AA, the second downgrade in nine months and two levels below its highest grade, with a negative outlook citing the nation's increasing debt burden.

U.S. debt has increased to 100 percent of gross domestic product, while debt climbed 23.6 percent from 2008 to 2010, the credit-rating firm said in a statement today. Egan-Jones lowered the U.S. grade to AA+ in a July. Treasuries have gained 4.6 percent since the company first lowered the U.S. rating, according to Bank of America Merrill Lynch index data.

The downgrade was based on "the increasing debt load coupled with the fact that there has been no tangible progress in addressing the country's growing debt to GDP" ratio, Sean Egan, president of Egan-Jones in Haverford, Pennsylvania, said today in a telephone interview. "Unfortunately, the debt is growing fairly rapidly while the GDP is not."