U.S. Treasury Secretary Jack Lew on Thursday maintained his forecast that U.S. borrowing capacity would last at least until late October, and added that the Treasury's cash balance would temporarily rise with Sept. 15 tax payments.

In a letter to U.S. congressional leaders, Lew urged them to raise the debt limit as soon as possible to avoid unnecessary risks to financial markets, to business and consumer confidence, and the U.S. credit rating.

"On July 29, I wrote to inform you that the extraordinary measures we have been employing to preserve borrowing capacity would not be exhausted before late October, and that they likely would last for at least a brief additional period of time. That continues to be our view, based upon our best and most recent information," Lew wrote.

Lew said the Treasury may again meet its goal of maintaining a $150 billion cash balance briefly in mid-September.

"We anticipate that it will rise temporarily after the September 15 deadline for corporate and individual tax receipts-possibly above $150 billion-and then will decline again," he wrote.