Dozens of nations sought ways to restart vital energy shipments through the Strait of Hormuz on Thursday after US President Donald Trump vowed more aggressive strikes on Iran, pushing oil prices back up with further pain to consumers.
Trump said operations would be intensified and gave no timeline for ending hostilities, drawing threats of retaliation from Tehran and sending share prices lower.
"We're going to hit them extremely hard over the next two to three weeks. We're going to bring them back to the Stone Ages where they belong," Trump said in a Wednesday evening speech.
Still defiant despite the death of a slew of its leaders, Iran said it was drafting a protocol with Oman on monitoring ships in the strait which carries about a fifth of the world's oil consumption in normal times but is now virtually closed.
"We are developing a protocol for Iran and Oman to monitor passage and navigation through the Strait of Hormuz", Deputy Foreign Minister Kazem Gharibabadi said, according to the official IRNA news agency.
"Of course, these requirements will not mean restrictions, but rather to facilitate and ensure safe passage and provide better services to ships that pass through this route."
In his speech, Trump suggested the war could escalate if Iran did not give in to Washington's terms during negotiations, with strikes on Iran's energy and oil infrastructure possible.
He told countries that rely on fuel shipments through the Strait of Hormuz to "just grab it". However, European and other states have said they will only help secure the strait if there is a ceasefire.
Britain chaired a virtual meeting of some 40 countries to explore ways to restore freedom of navigation, saying the focus was on diplomatic and economic tools.
"It can only be done in consultation with Iran," French President Emmanuel Macron said.
Iran threatens too
Iran's armed forces responded to Trump with a warning of "more crushing, broader and more destructive" attacks in store.
The war will continue until the "permanent regret and surrender" of Iran's enemies, said Ebrahim Zolfaqari, spokesperson for the Iranian military's Khatam al-Anbiya central headquarters, in a statement carried by Iranian media.
Iran's Fars news agency later listed several bridges in Saudi Arabia, Kuwait, Abu Dhabi and Jordan as potential targets for Iranian military operations. The Revolutionary Guards said they had targeted an Amazon cloud computing centre in Bahrain.
There are fears the conflict may leave Iran with a stranglehold over Middle East energy supplies now that it has shown that it can block the Strait of Hormuz by targeting oil tankers and attacking Gulf countries hosting US troops.
Gulf states say they reserve the right to self-defence but have refrained from responding militarily to repeated Iranian attacks over the past month, seeking to avoid escalation into a far more devastating all-out Middle East war.
Iran's parliament was reviewing a bill that would formalise the blocking of vessels from hostile countries passing through the strait and the charging of tolls for others wishing to pass, spokesperson Abbas Goodarzi said.
Finland President Alexander Stubb said on X he had discussed the situation in the Middle East with his Iranian counterpart Masoud Pezeshkian, urging a diplomatic solution.
"I emphasized the need to end the strikes on neighbouring countries and restore freedom of navigation in the Strait Hormuz," Stubb said. "Despite the disagreements, it is important to maintain dialogue."
'When over?'
Thousands of people have been killed across the Middle East since February 28, when the US and Israel began air strikes on Iran, triggering Iranian attacks on Israel, US bases and the Gulf states, while opening a new front in Lebanon.
Iran said several people were likely injured when a bridge linking Tehran and the western city of Karaj was hit by air strikes. Some of its largest steel producers and Tehran's Pasteur Institute of Iran medical research centre had sustained serious damage in the conflict, it said.
The Revolutionary Guards said they had targeted US-linked steel and aluminium facilities in Gulf states and would step up such attacks if Iranian industries were hit again.
Russia said it would ask the US and Israel to cease fire for its staff to leave Iran's Bushehr nuclear power plant.
Israel, which shoots down most Iranian missiles, reported new incoming salvoes on Thursday, Saudi Arabia said it had intercepted four drones and Abu Dhabi said it had intercepted a missile, with minor damage near an economic zone.
The U.S. embassy in Baghdad urged its citizens to leave Iraq, warning of attacks in the capital by Iran-allied militia in the next 24 to 48 hours.
Fuel shortages have already caused economic strains across Asia and are expected to bite in Europe soon, while a report by two UN agencies warned a sharp economic slowdown could spark a cost of living crisis in Africa.
Benchmark Brent crude prices jumped by about 7 per cent to around $108 per barrel, US bond yields spiked, and global equity markets gave back gains.
"The key question in all investors' minds is 'When is this going to be over?'" said Russel Chesler, Head of Investments and Capital Markets at VanEck Australia.