A credit rating firm has concluded a review of the United States' credit rating and reiterated that it deserves the highest rating.

Fitch Ratings had started a review of the U.S. debt rating in October and warned it might downgrade the nation's rating.

Fitch said Friday that the U.S. rating remains at "AAA." The agency adds that the debt-ceiling crises in 2011 and 2013 don't appear to have affected the country's ability to borrow. Fitch also says deficits that are expected to fall played a role in its decision.

Another ratings agency, Standard & Poor's, downgraded the U.S. credit rating one notch in 2011 after a standoff in Congress over whether to raise America's borrowing limit. S&P's rating remains at "AA+"