The U.S. military said it carried out strikes on Iranian military targets in response, although Tehran charged that it was Washington that had initiated the exchange of fire.

The latest violence threatens to unravel a fragile truce in effect since April 8 that brought an end to weeks of U.S.-Israeli attacks on the Islamic republic, which has retaliated with strikes across the Middle East and by blocking the strait, a vital route for oil and gas shipments.