The United States struck bridges and an airport in Iran on Friday, provoking Tehran to respond by hitting a power and desalination plant in Kuwait, as the warring foes risked further escalation by expanding their targets to include infrastructure.
At sea, where the renewed conflict has again cut off energy supplies from the Gulf, U.S. Marines boarded a tanker near the Strait of Hormuz. Another vessel was seized by armed men off Yemen, raising concern over security in the Middle East's other big choke point for oil shipments at the mouth of the Red Sea.
Washington and Tehran have been testing the limits of escalation since their ceasefire agreement collapsed last week, raising the prospect of a return to all-out war.
As reports of Friday's escalation emerged, benchmark Brent crude oil prices surged by more than 3% to near $87, the highest level since an interim agreement a month ago aimed at ending the war. Global share prices fell, with Wall Street opening sharply lower.