Fitch also said Spain will continue to face downgrade risks even if it avoids having to ask for a bailout, while Ireland could claw its way back into the single-A rating band if a deal is struck to share the burden of its banking debts.

Despite December's deal by US politicians to avoid the so-called "fiscal cliff" of spending cuts and tax hikes, Fitch's head of sovereign ratings, David Riley, said pressure on the country's rating was increasing.

Riley said the United States did not need the same kind of super-strength austerity some major developed economies are currently implementing because it was grinding out more economic growth than other high-debt nations.