NEW YORK (MarketWatch) -- Fitch Ratings put its AAA credit rating of the U.S. on negative watch Tuesday, citing the prolonged congressional negotiations over a hike to the borrowing limit. The U.S. is set to hit its debt ceiling on Thursday without a deal to increase its ability to borrow. "The prolonged negotiations over raising the debt ceiling (following the episode in August 2011) risks undermining confidence in the role of the U.S.dollar as the preeminent global reserve currency, by casting doubt over the full faith and credit of the U.S," the agency said in a statement. Senate Majority Leader Harry Reid had warned that a rating downgrade could come as soon as Tuesday.