Heightened worries that the U.S. and China are headed for a long standoff in their costly trade dispute put investors in a selling mood Thursday.

Stocks ended sharply lower on Wall Street in a broad sell-off that left the benchmark S&P 500 index on track for its third straight weekly loss and had the Dow Jones industrial average down more than 400 points until late afternoon.

Traders sought safety in the bond market, driving bond prices higher, which pulled the yield on the 10-year Treasury to 2.31%, the lowest level in more than a year.

The stock market has been highly volatile since Washington and Beijing escalated their dispute over trade earlier this month. Now, the two sides have broken off negotiations and appear set for a long standoff. Investors are concerned that a prolonged trade war could stunt economic growth and hurt corporate profits.

"Markets are appreciating how far apart the two sides are and how messy the grand deal would be that both sides had led us to believe was coming very quickly," said Sameer Samana, senior global market strategist at Wells Fargo Investment Institute.

The S&P 500 index fell 34.03 points, or 1.2%, to 2,822.24. The index was down 2.5% before the selling eased. The Dow lost 286.14 points, or 1.1%, to 25,490.47. At its lowest, the Dow slid 448 points.

The Nasdaq composite dropped 122.56 points, or 1.6%, to 7,628.28. The Russell 200 index of small company stocks gave up 30.25 points, or 2%, to 1,501.38.

Markets in Asia and Europe also saw steep losses.

The U.S. and China concluded their 11th round of trade talks earlier this month with no agreement. Instead, the U.S. moved to increase tariffs on Chinese goods, prompting China to reciprocate. The trade dispute escalated further after the U.S. proposed restrictions on technology sales to China, though it has temporarily backed off.

China is looking for ways to retaliate and has reached out for support from Russia and its neighbors in Asia. Both the U.S. and China have made overtures about continuing trade talks, but none are scheduled. That uncertainty has many traders nervous about how and when the trade dispute will be resolved.

"Now people are realizing how weighty the issue is and how many different aspects of it are just so intractable, where it's going to be difficult for the Chinese side to give in and it's going to be hard for the U.S. not to ask for some of these changes," Samana said.

The resumption of trade hostilities this month has interrupted a market rally that saw the S&P 500 wipe out the fourth quarter's sharp decline and hit a new high. The index is down 4.2% so far in May, though it's still sporting a gain of 12.6% for the year.

Trade-sensitive technology stocks led the market slide Thursday. Many tech companies do significant business in China, and the Trump administration's proposed restrictions on technology sales to Chinese companies hit their stocks hard.

Exxon Mobil fell 2.3% and Chevron gave up 2.2%, part of a broad slump in energy-sector stocks as the price of U.S. fell sharply. Benchmark U.S. crude plunged 5.7% to settle at $57.91 a barrel. It's down 7.8% for the week.

Investors sent shares in utilities and real estate companies higher. Those sectors are considered less risky, which makes them more attractive when traders are concerned about volatility and a slowdown in economic growth.