New Delhi, Aug. 1 -- TEHRAN - Oil prices rose Friday morning as word spread that Iran's Revolutionary Guards had struck two oil tankers attempting to transit the Strait of Hormuz under active United States air escort, the first such incident since Washington launched a convoy protection program for the waterway.

Iran's Islamic Revolutionary Guard Corps stated that the "non-compliant oil tankers" had been "struck and brought to a halt," while four additional vessels reversed course and withdrew from the Strait. The names of the struck vessels and any casualties were not immediately confirmed.

The incident challenged a program Washington has publicly championed as proof that US military presence can keep oil flowing through the contested ...