LONDON (AP) — The United States could lose its top credit rating for the second time from a leading agency if there's a delay in raising the country's debt ceiling, Fitch Ratings warned Tuesday.

Congress has to increase the country's debt limit, which effectively rules how much debt the U.S. can have, by March 1 or face a potential default. There are fears that the debate will descend into the sort of squabbling and political brinkmanship that marked the last effort to raise the ceiling in the summer of 2011. The U.S. Treasury Department warned then that it had nearly reached a point where it would be unable "to meet our commitments securely."

"The pressure on the U.S. rating, if anything, is increasing," David Riley, managing director of Fitch Ratings' global sovereigns division said at a London conference. "We thought the 2011 crisis was a one-off event .... if we have a repeat we will place the U.S. rating under review."