- The S&P 500 and the Nasdaq composite fell 1.4 percent and 2.1 percent, respectively. The S&P also broke below its 50-day moving average, a key technical level.
- The CBOE Volatility Index (VIX), widely considered the best gauge of fear in the market, hit its highest level since May.
U.S. equities fell the most since May on Thursday as tensions between the United States and North Korea persisted.
The Dow Jones industrial average fell 204.69 points to close at 21,844.01, with Goldman Sachs contributing the most losses. That was its biggest point loss since May 17.
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The declined 1.45 percent to end at 2,438.21, with information technology and financials leading the way lower. It was the benchmark's worst percentage drop since a 1.8 percent decline on that same day in May. The index also dipped below its 50-day moving average, a key technical level, for the first time in a month.
The Nasdaq composite lagged, pulling back 2.13 percent to 6,216.87, with Apple, Alphabet, Amazon and Netflix all trading lower.
"If you look across all sectors, it's a broad-based sell-off," said Paul Springmeyer, investment managing director at U.S. Bank's Private Client Reserve. "The news is concerning to all. ... I think this is a cautious pullback."
The CBOE Volatility Index (VIX), widely considered the best gauge of fear in the market, soared more than 40 percent to trade at 15.98. It also hit its highest level since May.
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Earlier this week, President Donald Trump said that North Korea would face "fire and fury" if it continued to threaten the States, however North Korea has dismissed these warnings by the U.S. incumbent as a "load of nonsense."
Trump doubled down on his remarks Thursday, saying his previous statement may not have been tough enough.
"I think this is normal market action for this time of the year," said Phil Blancato, CEO of Ladenburg Thalmann Asset Management. "People are taking profits off the table" with the U.S.-North Korea situation hanging over the market.
The iShares MSCI South Korea capped exchange-traded fund (EWY), which tracks South Korean stocks, fell 2.4 percent Thursday.
Traditional safe havens have seen solid inflows as tensions have increased. Gold futures have risen more than 2 percent this week, while the Swiss franc has advanced 0.9 percent against the U.S. dollar. On Thursday, gold futures jumped about 1 percent and hit their highest level in two months.
"We're through most of the earnings season and the valuations [in the stock market] become a bit problematic when you have something like North Korea come up," said Maris Ogg, president at Tower Bridge Advisors.
Equities, meanwhile, have slipped across the world but hadn't posted a meaningful pullback since the two nations started taking verbal jabs at each other.
The S&P was only down 0.1 percent for the week entering the session. In Europe, the Stoxx 600 index has fallen 1.2 percent for the week.
"Our assumption is that the 'battle of the bombasts' will remain verbal for the foreseeable future and that Guam will drop out of the headlines as quickly as it has been inserted into them," Michael Shaoul, chairman and CEO of Marketfield Asset Management, said in a note.
"It remains possible that we will see another brief lurch downwards, particularly in the technology sector that seems to be the locus of hedging activity, but the chances of this developing into a meaningful correction still looks remote at the current time," Shaoul said.
Investors also kept an eye on tech stocks, as the year's best-performing sector dropped more than 1 percent.
The sector "seems a little crowded," Darrell Cronk, president at Wells Fargo Investment Institute, told CNBC's "Squawk on the Street." "When you look at active managers' positioning today, they are 30 percent over-positioned to a historical norm."
Wall Street also turned its eyes to retail earnings, as Macy's and Kohl's both reported better-than-expected quarterly results. Dillard's, however, posted much weaker-than-expected results, sending the stock down 16 percent.
Calendar second-quarter earnings have been mostly better than expected, with growth surpassing initial expectations and most S&P 500 companies topping profit and sales estimates.
The positive earnings helped lift U.S. stocks to record highs. Last week, the Dow broke above 22,000 for the first time.
—CNBC's Alexandra Gibbs contributed to this report.