He did not present any evidence to back up that claim, which is certain to further heighten tensions between the Trump administration and Iranian leaders. The United Nations secretary general expressed “deep concern” that the new episode might lead to a military escalation.

What happened: Crews abandoned both ships, one of which caught fire, early in the morning, but other details remained murky. The attack came a month after four tankers were damaged in the same area.

Footage: A U.S. Navy surveillance plane flying over the two tankers on Thursday spotted an unexploded mine attached to the hull of one of the ships. It resembled the kind of explosive that investigators believe was used against the four ships in the attacks last month, an official said.

Industry impact: Oil prices rose more than 3 percent after the ships were struck just outside the Strait of Hormuz, a narrow conduit for about a third of the world’s crude oil.