Fitch Ratings on Monday affirmed its top-rung AAA investment-grade ratings for the United States' long-term debt, and assigned a stable outlook.

Despite looming challenges from the government's indebtedness, a Fitch analyst said that the near-term risk to the 'AAA' status is "minimal."

Brian Coulton cited the U.S.' "exceptional financing and economic flexibility, and the U.S. dollar's role as the world's predominant reserve currency."

Coulton added, "However, difficult decisions will have to be made regarding spending and tax to underpin market confidence in the long-run sustainability of public finances and the commitment to low inflation."

Fitch affirmed AAA ratings for the U.S.' long-term foreign and local currency issuer default ratings, or IDRs, with a stable outlook. Fitch also affirmed the U.S.' country ceiling at 'AAA' and the short-term foreign currency rating at F1+, Fitch's top short-term rating.

Coulton said U.S. efforts to lift its economy out of recession through financial rescue and stimulus programs "now appear to be working in terms of restoring stability to the U.S. financial sector and the economy."

However, if deficit-reduction measures don't take hold over the next three to five years, government indebtedness "will approach levels by the latter half of the decade that will bring pressure to bear on the U.S.' 'AAA' status," Coulton said.

Fitch estimated the general government deficit at 11.4 percent of gross domestic product in 2009, and forecasts 11 percent this year and 8.5 percent next year.

That deficit, Fitch said, contains "a sizeable structural component that will not be eliminated by the economic recovery and the unwinding of stimulus measures."