U.S. stocks open lower after Fed official's comments

U.S. stocks opened lower on Friday, as investors became cautious amid comments by a U.S. Federal Reserve official.

Boston Fed President Eric Rosengren said in a speech low interest rates are increasing the chance of overheating the U.S. economy, according to the CNBC. Gradually tightening monetary policy is appropriate to maintaining full employment, he added.

The Federal Open Market Committee, the Fed's monetary policy arm, is set to meet on Sept. 20-21.

Newly-released data, including nonfarm payrolls report last week, has been in focus recently, with investors pondering over when the central bank will decide to raise interest rates.

The current expectations for a September rate hike stand at 18 percent, according to CME's FedWatch tool.

Shortly after the opening bell, the Dow Jones Industrial Average shed 137.82 points, or 0.75 percent, to 18,342.09. The S&P 500 lost 17.88 points, or 0.82 percent, to 2,163.42. The Nasdaq Composite Index decreased 38.15 points, or 0.73 percent, to 5,221.33.

U.S. stocks ended lower on Thursday, with the Nasdaq snapping four-day winning streak, as investors mainly digested weekly jobless claims and a decision from the European Central Bank (ECB). Endi