Stock market extends losses after worst one-day tumble in 3 months

U.S. stock-index benchmarks opened lower on Friday, extending the prior session's selloff that was partially fueled by a terrorist attack in Barcelona and rumors that an economic adviser to President Donald Trump might resign.

The Dow Jones Industrial Average traded 13 points, or less than 0.1%, lower to 21,735, while those for the S&P 500 index slipped 2 points, or less than 0.1%, to 2,428. The Nasdaq Composite Index retreated 3 points, or 0.1%, at 6,218. Gains in shares of chip-equipment supplier Applied Materials Inc.(AMAT), up 4.4%, were helping to limit the tech-heavy Nasdaq's losses after it reported better-than-expected quarterly results.

The retrenchment for stocks comes after one of the sharpest downturns of 2017, when the S&P 500 index slumped 1.5% for its biggest one-day percentage drop in three months. The Dow average and Nasdaq Composite Index ended down 1.2% and 1.9%, respectively.

The benchmarks are now on track for weekly losses around 0.5%. The Dow is on pace for its largest two-week percentage decline since mid-September last year, while the Nasdaq is flirting with its longest weekly losing streak since May 2016, as it has fallen for four weeks in a row.

"In a week where we started by worrying about nuclear war, markets have quickly moved on from this, with yesterday's weak session more of a response to fears that Mr. Trump's strategy for the economy and business is falling apart," strategists at Deutsche Bank said in a note.

Market participants are still focused on the terror attack in Spain, which happened on Thursday , with a van plowing into crowds in one of Barcelona's busiest venues, killing at least 14 people and injuring scores. Islamic State has claimed responsibility for the terror attack. Hours after the Barcelona incident, police killed five alleged terrorists following a separate attack that hurt seven people in Cambrils, a Spanish town southwest of Barcelona.

European stocks were sharply lower on Friday following the attacks. Spain's IBEX 35 index was among the hardest hit, down 1% at 10,342.20.

Also spooking investors were reports on Thursday that Gary Cohn was planning to resign as an economic adviser to the president. The White House has countered those rumors.

Cohn is "seen as the glue holding Trump's pro-business agenda together," Deutsche Bank's strategists said. "The fears are that if he goes, you take a further step back from tax cuts and deregulation."

The dollar was trading lower on Friday. The ICE Dollar Index was down 0.2% at 93.480.

Stock movers: Shares in Ross Stores Inc.(ROST) rallied 11% after the off-price retailer late Thursday reported earnings and sales above forecasts.

Calpine Corp.(CPN) soared 11% in premarket trade after a Wall Street Journal report late Thursday said Energy Capital Partners is closing in on a $17 billion deal to acquire the power company.

U.S.-listed shares of Infosys Ltd.(500209.BY) slid 8.9% after Vishal Sikka on Friday resigned as chief executive.

Foot Locker Inc. (FL) plunged 25% after the sports-apparel company significantly missed profit forecasts.

Deere & Co.(DE) opened at a three-month low, with shares down 7% after quarterly sales at the farming-equipment company missed expectations.

On an upbeat note in Friday's earnings, Estée Lauder Cos.(EL) climbed 4.7%. Both earnings and profit at the beauty company beat estimates.

Economic news: A consumer sentiment reading for August is due at 10 a.m. Eastern Time.

On the Federal Reserve front, Dallas Fed President Robert Kaplan is due to speak at a community college event in Dallas at 10:15 a.m. Eastern.

Other markets:Asia markets closed broadly lower, with Japan's Nikkei 225 index finishing at a three-month low.

Oil prices traded slightly higher on Friday, rising 0.2% to $47.19 a barrel. Metals were higher across the board, with gold added 0.7% above $1,300 an ounce on increased haven demand.

By Sara Sjolin, MarketWatch