Iran targeted US radar and air defence installations in the Gulf on Tuesday, warning Washington of "more decisive and powerful" attacks to come as the conflict threatened to widen with a blockade of Saudi ports by Houthi rebels in Yemen.
Tehran's Yemeni allies, the Houthi rebels, meanwhile threatened a major broadening of the war, announcing they would blockade Saudi ports.
Such a move by the Houthis would put at risk Riyadh's ability to bypass the flashpoint Strait of Hormuz for some of its oil exports and have major repercussions on the global economy.
Saudi Arabia and the Houthis traded fire last week for the first time in years, threatening a 2022 truce, but the rebels have largely remained on the sidelines since Israel and the United States attacked Iran in late February.
Saudi Arabia strongly condemned the threat from what it called the "terrorist Houthi militia" and said it "continues to support the brotherly Yemeni people and their legitimate government".
The Middle East war resumed after an April ceasefire and a June framework deal collapsed.
Agence France-Presse