Stock futures were mixed in early trading Wednesday after a losing session, with Dow Jones Industrial Average futures down just under 0.1%, S&P 500 futures advancing less than 0.1%, and Nasdaq 100 futures adding 0.16%. The Dow dropped 1.2% on Tuesday, its worst day in almost three weeks, while the S&P 500 and Nasdaq Composite slid 0.6% and 0.3% respectively. Oil prices surged as escalating tensions between the U.S. and Iran fueled concerns over Middle East energy supply disruptions.

Brent crude futures rose more than 2% to break $100 a barrel for the first time since July, trading at $100.02 by 3:35 a.m. ET. The 10-year U.S. Treasury yield briefly climbed above 4.8% on Tuesday, adding to inflation concerns. Kara Murphy, investment chief at Kestra Investment Management, called it "a little bit of a speed bump" on CNBC's "Closing Bell." No major economic data or earnings are due Wednesday; traders will watch inflation readings later this week for Federal Reserve signals.

In Asia, Japan's Nikkei 225 closed 0.19% lower at 65,142.78, South Korea's Kospi rose 1.40% to 7,051.64, and Australia's S&P/ASX 200 fell 0.11% to 8,911.40. European markets opened lower, with the Stoxx 600 down 0.49%. Ørsted shares fell 1.9% after Andel Holdings announced plans to sell about 3 billion Danish kroner ($467.1 million) of its stake.