Source: Sharecast
As of 1255 BST, Dow Jones futures were down 1.10%, while S&P 500 and Nasdaq-100 futures had the indices opening 0.92% and 1.40% lower, respectively.
The Dow closed 130.76 points lower on Tuesday, taking a bite out of solid gains recorded in the previous session.
US Central Command said late on Tuesday that American forces had launched a "series of powerful strikes" against Iran in response to alleged attacks on three commercial vessels travelling through the Strait of Hormuz. Earlier, the Treasury revoked a licence that had allowed Iran to sell oil globally following the incidents.
Iran's foreign ministry condemned the strikes as a "gross violation" of last month's memorandum aimed at ending hostilities, stating its armed forces would not hesitate to defend the country's sovereignty.
NATO Secretary General Mark Rutte backed the US response, telling reporters in Ankara that the strikes were "absolutely necessary" given Iran's actions.
Oil prices surged on the news, with international benchmark Brent crude futures up 5.7% at $78.39 a barrel and West Texas Intermediate rising 5.61% to $74.39 a barrel.
Market participants will also be zeroed-in on minutes from the Federal Reserve Open Markets Committee's latest policy meeting, scheduled for release at 1900 BST, with the minutes expected to provide further insight into chairman Kevin Warsh's first meeting, where policymakers kept interest rates unchanged and indicated that additional interest rate hikes may be warranted if inflationary pressures persist.
Elsewhere on the macro front, US mortgage applications fell by 2.2% on the week ended 3 July, according to the Mortgage Bankers Association. Last week's modest decline came amid relative stability in benchmark mortgage rates, with the 30-year fixed rate rising just a single basis point to 6.58%, despite an increase in longer-term Treasury yields during the week. Applications to refinance a mortgage, which are more sensitive to week-to-week changes in interest rates, fell by 4.1%, while applications to purchase a home inched down by 0.6%.
Still to come, May wholesale inventories figures were slated for release at 1500 BST, while May consumer credit change numbers will follow at 2000 BST.
In the corporate space, iconic jeans maker Levi Strauss was slated to report earnings after the close of trading.
Reporting by Iain Gilbert at Sharecast.com