New Delhi, July 3 -- Iran's joint military command warned Thursday that all oil tankers moving through the Strait of Hormuz must use its approved routes or face a "forceful response," ratcheting up tensions again over a waterway crucial for international energy supplies.

The strait, the narrow mouth of the Persian Gulf, has emerged as one of the top issues in negotiations seeking a permanent end to the Iran war. The statement from the Khatam al-Anbiya military command, reported by Iranian state television, comes after both U.S. and Iranian diplomats met with mediators Wednesday in Qatar.

Iran is preparing for the funeral of the late Supreme Leader Ayatollah Ali Khamenei, who was killed in the war's first moments in February. On Thursday...