Saudi Arabia shut its East-West pipeline, a route that lets Gulf oil avoid the Red Sea, after a drone launched from Iraqi territory hit it.
Iran says it attacked US military bases in Bahrain, Jordan and Iraq, and the United States and Iran have gone back to trading attacks after a short pause in fighting.
Iran launched a new round of missile attacks, and United States and Saudi Arabian forces struck Iran-backed militia groups in Iraq, according to news reports.
Saudi Arabia has for the first time taken part directly in air strikes alongside the United States, hitting an Iraqi militant alliance linked to Iran on July 29.
Days after signs Iran's conflict with the US was cooling, fighting flared again on three fronts: Iran fired a missile attack on US forces, which the US says it intercepted; US and Saudi jets bombed Iran-backed militants in Iraq who had launched drone attacks; and Iran's Revolutionary Guards seized three oil tankers in the Strait of Hormuz, a narrow sea passage carrying much of the world's oil.