The Iran-backed Houthi rebels have attacked several cities in Saudi Arabia, wounding 73 people and knocking operations at energy facilities offline, the Saudi-led coalition said on Tuesday in a further sign of the conflict spreading as diplomacy stalls. The coalition vowed a firm response to attacks on the southern cities of Abha, Khamis, Mushait, Jazan and Najran, as the country’s energy ministry said a number of facilities had been hit, causing fires and temporarily halting some operations. Houthi spokesperson Yahya Sarea said that the Yemeni group would soon announce a broad military operation “deep” into Saudi Arabia. The Houthis, who control the most populous parts of Yemen and much of the north, have been launching attacks towards Saudi Arabia since they declared a naval blockade against Riyadh in July, with strikes targeting its vessels in the Red Sea. Iran meanwhile threatened the US with “economic warfare” on Tuesday and said that it had fired an advanced missile at US warships. Tehran has vowed to announce a new restricted zone in the Gulf in the coming days in an effort to further squeeze shipping through the Strait of Hormuz, driving up oil prices and piling pressure on US president Donald Trump to end the war. Houthis attack Saudi Arabia and wound dozens as conflict widens: Live