Yellen warns lawmakers U.S. Treasury to hit debt limit Oct. 18

U.S. Treasury Secretary Janet Yellen on Tuesday again warned lawmakers that the nation was close to exhausting its federal borrowing capabilities - now set for Oct. 18 - and urged Congress to act in order to avert "serious harm" to the economy.

"At that point, we expect Treasury would be left with very limited resources that would be depleted quickly," she wrote in her latest letter to congressional leaders.

"It is uncertain whether we could continue to meet all the nation's commitments after that date," she added in the letter, one day after Senate Republicans rejected a measure to raise the nation's borrowing limit to pay for previously incurred government spending.

The Treasury had already enacted "extraordinary measures" to keep government funds flowing after the debt ceiling was reached over the summer. But those measures will run out in about 20 days, although the exact date could vary, Yellen said.

"This uncertainty underscores the critical importance of not waiting to raise or suspend the debt limit," she said.