Safe haven assets rose and Japanese and South Korean stocks plunged as North Korea said it was considering an attack on the U.S. territory of Guam after President Donald Trump promised to respond to continued threats with "fire and fury."

Tokyo's Nikkei 225 index closed down 1.29%, while South Korea's Kospi Composite slid 1.1%. The Swiss franc gained more than 0.9% to CHF0.96 to the dollar by 4 a.m. ET. The FTSE 100 fell 0.5% and stocks retreated by at least 0.8% in Paris and Frankfurt. Gold futures rose 0.9% to $1,273.5 an ounce.

According to a Bloomberg News report that was updated recently, gold surged 1.1% to $1,274.37 an ounce, the biggest rise in two months, and West Texas Intermediate crude increased 0.8% to $49.58 a barrel.

Meanwhile, the U.S. stock market opened lower on Aug. 9, with the Dow Jones Industrial Average down 0.25% to 22,029.58 and NASDAQ down 0.49% to 6,339.55 around 10:54 a.m. ET and the S&P 500 down 0.22% to 2,469.50 before that time. The FTSE 100 Index declined 0.56% to 7,500.31 and France's CAC 40 lost 1.42% to 5,144.83 around 10:34 a.m. ET.

Switzerland's franc jumped 1.4% to 0.9611 francs per euro in early trades, marking the biggest single-day rise against the euro since January 2015, Reuters reported.