WASHINGTON Wall Street executives who have advised the U.S. Treasury's debt operations for the past 25 years warned on Tuesday they are "deeply concerned" about the debt limit impasse that has markets worried about a U.S. default on payment obligations.

The 18 current and former chairs and vice chairs of the Treasury Borrowing Advisory Committee said in a letter to Treasury Secretary Janet Yellen that "any delay in making an interest or principal payment by Treasury would be an event of seismic proportions, not only for financial markets but also the real economy."

(Reporting by David Lawder; Editing by Sandra Maler)