Two weeks since the effective collapse of an interim truce meant to end the war, the US military launched another nightly round of air strikes on Iran, prompting Iran to fire at neighbouring Arab countries that house US bases.
US Secretary of State Marco Rubio told a diplomatic gathering in Southeast Asia the price Iran pays "will get higher every night" until Tehran was ready for a peace deal it would live by.
"Iran is begging (for a deal) every day. The problem with Iran is every time they make a deal ... they either break it or they want to change it," he said on Thursday.
"So now they're paying the price for it. And maybe they'll change their mind here over the next few days as they continue to suffer great losses."
The Houthis, fighters allied to Iran who control Yemen's Red Sea coast, said this week they were imposing a blockade on Saudi Arabia, which has diverted millions of barrels of oil per day by pipeline to the Red Sea to get around Iran's blockade of the Gulf.
In their first such strikes since announcing the move, the Houthis said their forces had carried out missile and drone strikes on two Saudi oil tankers, identifying them as the Encelia and the Layla.
A maritime security source said the Encelia had transmitted a distress call reporting it had been struck by a missile near the Saudi port of Jizan in the Red Sea just north of Yemen late on Wednesday.
Saudi state news agency SPA said the strike had caused a fire at the bow.
Reuters could not immediately confirm the other attack, on the Layla.
Houthi attacks on tankers could effectively close the Bab el-Mandeb strait - the "Gate of Tears" - which controls access from the Red Sea to the Indian Ocean, the second most important waterway for energy markets after the Strait of Hormuz at the mouth of the Gulf.
Meanwhile, Iran said it attacked US missile systems, weapons and fuel storage sites in Jordan, as well as US military posts in Kuwait.
It has also hit water desalination and energy plants in Kuwait this week.
Iranian military spokesperson Brigadier General Mohammad Akraminia said Iran would keep retaliating as long as the US continued to attack its infrastructure and coastal areas, Iranian state TV reported.
High oil prices are stoking inflation globally, and have put President Donald Trump's Republican allies under pressure before congressional elections in November.
In the days since the Houthis announced their blockade in the Red Sea, several tankers have already changed course to avoid the Bab el-Mandeb, heading north instead through the Suez Canal, potentially using a much longer and more expensive route to reach Asian customers by sailing around Africa.
The Houthi threat to impose a naval blockade against Saudi Arabia could significantly widen the war and strain the US military, current and former US officials said.
Rubio said the Houthis got "snookered into this" by Iran, expressing hope the situation would de-escalate soon.
June's interim deal to halt fighting has collapsed over the Strait of Hormuz, where Iran aims to assert control by requiring ships to sail close to its coastline and eventually charge transit fees.
It has fired on ships using an alternative channel further from its coast, promoted by Washington.
Trump vowed on Wednesday to destroy an Iranian bridge or power plant every time Iran shot at a ship in the Strait of Hormuz.
Iran's joint military command in turn warned it would target regional oil, gas, electricity and economic infrastructure and prevent the export of "even a single drop of oil", Iranian state media reported.
