Sri Lanka, July 15 -- Two oil tankers came under a suspected attack Thursday near the strategic Strait of Hormuz, with one of them set ablaze, and the U.S. blamed Iran in what it called a campaign of "escalating tensions" in a region crucial to global energy supplies.

The U.S. Navy rushed to assist the stricken vessels in the Gulf of Oman off the coast of Iran. The ships' operators offered no immediate explanation on who or what caused the damage against the Norwegian-owned MT Front Altair and the Japanese-owned Kokuka Courageous. Each was loaded with petroleum products, and the Front Altair burned for hours, sending up a column of thick, black smoke.

U.S. Secretary of State Mike Pompeo said the U.S. assessment of Iran's involvement was...