Iran's Revolutionary Guards reported that two oil tankers carrying more than two million barrels of crude oil each caught fire after hitting naval mines in the Strait of Hormuz.
The waterway normally carries about one-fifth of global oil consumption, and Iran has seized control of it following the start of the West Asia war in late February.
Security data showed six vessels were attacked in or near the strait on Sunday, marking the highest single-day attack total since the conflict began.