All the 11 major S&P indexed were lower, with technology sector's 0.62 percent leading the decliners. In Asia, markets were mostly lower after disappointing Chinese trade data.
Chinese stocks seemed little affected though, and Australian stocks rose Wednesday after a weaker Tuesday amid strong earnings reports from big banks.
European shares were also lower following reports that a vehicle had rammed a group of soldiers in Paris, injuring six before speeding off in what officials identified as a suspected terrorist attack.
US stock indexes opened lower on Wednesday as investors turned risk averse.
Stocks are ending broadly lower on Wall Street, led by declines in technology companies and banks, two of the highest-performing sectors over the past year. Sony Corp. shares in Tokyo dropped 1.6 percent.
Trump doubled down on his remarks Thursday, saying his previous statement may not have been tough enough.
Trump was responding to North Korea's claim it was completing plans to fire four intermediate-range missiles over Japan to land near the US Pacific territory of Guam.
BONDS: Bond prices rose.
The market's main backstop in times of strain, gold, hit a two-month high of $1,282 an ounce amid the nervousness. The Dow Jones industrial average fell 0.17 percent, with the tech-heavy Nasdaq composite index declining 0.28 percent.
Macy's (M.N) shares closed down 10.2 percent and Kohl's (KSS.N) fell nearly 6 percent as the companies continued to report a drop in quarterly same-store sales, stoking concerns that their turnarounds may still be a long way off.
Investors fled to gold on Wednesday as tensions between North Korea and the U.S. escalated, pushing the precious metal's price to an intraday high of $1276.2/oz.
"At least in this segment, investors apparently remain reluctant to seek gold's safe haven".
Among European markets, Britain's FTSE 100 fared the worst, down 1.10% as 80% of index members tumbled, led by the telecommunication sector.
The Canadian dollar was trading at an average price of 78.67 cents USA, down 0.04 of a US cent. The yield on the 10-year Treasury note slipped to 2.21 percent from 2.25 percent late Wednesday. The September copper contract was down two cents to $2.91 a pound. On the Nasdaq, 1,685 issues fell and 615 advanced favoring decliners.
"The markets are looking for direction after Wednesday's sharp moves and geopolitical concerns will dominate investor mindsets in the coming days", said Esther Maria Reichelt, an FX strategist at Commerzbank in Frankfurt.