The rating agency Fitch downgraded the US government's top credit rating on Tuesday, a move that drew an angry response from the White House and surprised investors.

Fitch downgraded the United States to AA+ from AAA, citing fiscal deterioration over the next three years and repeated down-the-wire debt ceiling negotiations that threaten the government's ability to pay its bills. It is the second major rating agency after Standard & Poor's to strip the US of its triple-A rating.