The blockade, announced by U.S. Central Command, will affect vessels entering or leaving Iranian ports.
Trump has warned Iran that the U.S. could set the country 'back to the stone ages,' including targeting power plants and bridges.
President Trump voices frustration with allies as Iran war, strait closure pushes fuel prices higher
Spot prices of Brent crude, the international standard, hovered around $106 a barrel Tuesday, up more than 45% since the war started Feb. 28.
His first statement since his appointment was read on state television Thursday by a news anchor.
Iran has attacked commercial ships across the Persian Gulf and targeted Dubai International Airport.
In addition to striking Tehran on the fifth day of the conflict, Israel hit the Iranian-backed Hezbollah militant group in Lebanon.
Qatari Foreign Ministry spokesman Majed Al Ansari vowed that Iranian attacks on the gas-rich country “will not go unanswered.”
The assassination of the second leader of the Islamic Republic, who had no designated successor, would throw its future into doubt.
Iranian President Ebrahim Raisi, the country’s foreign minister and others have been found dead at the site of a helicopter crash.