A focal point of the Iran war is increasingly about who controls the Strait of Hormuz — a narrow, elbow-shaped waterway that for decades was a relatively safe and reliable transit route for Middle East oil and natural gas supplies.

By saying that an interim ceasefire gave it the right to establish the terms under which ships traversed the strait, and threatening and firing upon vessels that did not use its preferred route, Iran has sought to exert control over the waterway and gain negotiating leverage with the United States.