Lew: Raise debt limit to stop 'unnecessary risks'

U.S. Treasury Secretary Jack Lew on Thursday reaffirmed his view that the government could stay funded by extraordinary measures through late October, but urged Congress to raise the borrowing limit and avoid unnecessary turmoil.

In a letter, Lew noted that the Treasury will reach its borrowing capacity once it exhausts emergency options. The department has implemented various measures, such as suspension of certain investments, to pay government bills ahead of the Sept. 30 deadline to extend spending authority.

"In the past, failure to raise the debt limit in a timely manner has negatively impacted business and consumer confidence, financial markets and the credit rating of the United States. To avoid these unnecessary risks, I respectfully urge Congress to raise the debt limit as soon as possible," Lew wrote.

Read MoreProspect of another shutdown looms

The government was previously shut down in 2013 amid attempts to defund the Affordable Care Act. An impasse over Republican attempts to block Planned Parenthood funding has raised concerns about the government's spending authority expiring again.

This week, Goldman Sachs Global Macro Research contended in a note that a government shutdown "appears nearly as likely as not." However, it said the incident may only have a "modest" effect on markets.