WASHINGTON The U.S. Treasury Department reiterated Monday it expects to be able to pay the U.S. government's bills only through June 1 without a debt limit increase, leaving just 10 days for congressional Republicans and White House negotiators to reach a deal.

In her third letter to Congress in three weeks, Treasury Secretary Janet Yellen said it was "highly likely" that the agency will be unlikely to meet all U.S. government payment obligations by early June, triggering the first-ever U.S. default.

The debt ceiling could become binding by June 1, she said.

Yellen's letter reflects further data on revenues and payments received since she told Congress on May 15 that Treasury would likely run out of cash to pay government bills in early June, and potentially as early as June 1.

(Reporting by Andrea Shalal and David Lawder; editing by Heather Timmons)