A fresh batch of retail earnings is in focus, too, with Dillard's among several stocks within the sector set to plunge after reporting.
Pyongyang said it was examining plans for attacking Guam, a USA territory in the Pacific that has a US military base.
"That may have weighed a little bit" on markets, said Phil Guarco, global investment specialist JP Morgan Private Bank.
BONDS: Bond prices rose. As a result, the yield on the benchmark ten-year note, which moves opposite of its price, fell by 2.9 basis points to 2.212%.
The market indexes wavered between small gains and losses for much of the morning, then veered lower by afternoon.
South Korea and the North technically remain at war as the Korean War ended only with an armistice, not a peace treaty.
North Korea said on Wednesday it is considering plans for a missile strike on the US Pacific territory of Guam, just hours after President Donald Trump told the North that any threat to the United States would be met with "fire and fury".
As stocks have fallen, the CBOE Volatility Index, which measures investors' expectations for swings in the S&P 500, has climbed.
Traders snapped up shares in companies that delivered strong quarterly results.
Retailers were also falling Thursday.
Guam´s local population numbers 162,000 and its economy depends primarily on tourism and the US military
Still, even with the week's moves, US stocks remain near their all-time highs. The Dow is now 0.9% off its closing record, while the S&P 500 is 1.3% off and the Nasdaq is 2.7% off their respective closing records.
Health care equipment and services company Henry Schein declined amid a broader slide by health care stocks.
Sterling GBP= was last trading at $1.3006, up 0.02 percent on the day.
The Canadian dollar gave back 0.1 cents to 78.68 cents U.S. Brent crude, the worldwide standard, lost 23 cents to $52.14 a barrel in London. Netflix was down 1.8 per cent. Heating oil fell one cent to 1.63 a gallon. Travel-review website operator TripAdvisor was down 2.7 per cent. USA gold futures GCcv1 gained 1.63 percent to $1,283.20 an ounce.
In other precious metals, silver rose 0.8% to US$17.04 per ounce, after hitting its highest since June 15 earlier in the session.
Charter Communications rose 2.9 per cent on news Altice is exploring a bid for the cable giant.
The dollar was steady at 110.030 yen after going as low as 109.560 overnight, its weakest in eight weeks.
Separately, U.S. producer prices unexpectedly fell in July, recording their biggest drop in almost a year, weighed down by declining costs for services and energy products. Britain's FTSE 100 added 0.1 percent.
USA stocks closed slightly lower Wednesday, making up much of the ground they lost earlier after a rare batch of earnings disappointments by Walt Disney and other big companies.
Dow Jones Industrial Average (DJIA) futures are trading below fair value, as the tensions between the USA and North Korea amplify.
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