U.S. stocks retreated, following the biggest weekly rally since January 2013, as energy producers led losses after oil dipped below $80 a barrel.

Halliburton Co., Newfield Exploration Co. and Nabors Industries Ltd. fell more than 5.5 percent to lead losses in energy companies. Merck & Co. slid 2.8 percent after cutting the top end of its sales forecast. Sarepta Therapeutics Inc. plunged 36 percent after saying regulators require more data on a new drug proposal.

The Standard & Poors 500 Index slipped 0.3 percent to 1,958.51 at 12:47 p.m. in New York. Equities pared losses after the European Central Bank said it settled 1.704 billion euros ($2.2 billion) of covered-bond purchases last week as it started its latest effort to revive the euro-area economy. The Dow Jones Industrial Average was down 32.65 points at 16,772.76. The Russell 2000 Index retreated 0.5 percent.

Source : Bloomberg