Iran vowed Thursday to make the United States regret launching its war against the Islamic republic, and said it would keep up its chokehold on the Strait of Hormuz as oil prices soared.
The International Energy Agency warned the Middle East war could lead to "the largest supply disruption" in oil industry history, but US President Donald Trump wrote on social media that defeating Iran's "evil empire" was more important than crude prices.
Trump has faced intense political pressure as the global economic fallout of the crisis has mounted, and he has given repeated mixed messages as to when the US campaign might end.
"While starting a war is easy, it cannot be won with a few tweets. We will not relent until making you sorry for this grave miscalculation," Iranian security chief Ali Larijani said on X.
His comments came after Iran's new supreme leader, Ayatollah Mojtaba Khamenei, issued a defiant statement -- his first since being appointed last Sunday after the death of his father and predecessor Ali Khamenei in a strike.
Mojtaba Khamenei, who was reportedly also wounded, has yet to appear publicly since his nomination, and his message calling for vengeance was read by a newscaster on state television.
"The lever of blocking the Strait of Hormuz must definitely be used," Khamenei said of the waterway through which a quarter of the world's seaborne oil trade usually transits.
The Revolutionary Guards reacted swiftly, with the force's navy commander Alireza Tangsiri saying: "In response to the order of the commander-in-chief, we will deliver the harshest blows to the aggressor" while keeping Hormuz closed.
The strait, which also normally sees the transit of a fifth of the world's liquefied natural gas (LNG), lies off Iran and is just 54 kilometres (34 miles) wide at its narrowest point.
As oil prices rose above $100 a barrel, Trump said that "of far greater interest and importance to me, as President, is stoping an evil Empire, Iran, from having Nuclear Weapons, and destroying the Middle East and, indeed, the World".
In an interview with AFP, Iran's deputy foreign minister Majid Takht-Ravanchi said Tehran was only acting in "self defence" and wanted to ensure that war could not be "imposed" on it again.
Takht-Ravanchi confirmed that Iran had been approached by some "friendly countries" to put an end to the conflict, without specifying which ones.
"We are telling them the same thing, that we want the ceasefire to be part of an overall formula for ending the war altogether," he added.
Pierre Razoux, director of studies at the Mediterranean Foundation for Strategic Studies, said that Iran "no longer has anything to lose" and would "wage a war of attrition against the United States and Israel".
"If the White House imagines the conflict will stop when Donald Trump decides it... they're making a mistake and ignoring the lessons of history," he told AFP.
Gulf states have borne the brunt of retaliatory attacks from Iran.
Images from Bahrain on Thursday showed thick smoke rising after a strike on fuel tanks in Muharraq, with residents told to stay inside and close their windows.
Drones caused damage again at Kuwait's international airport and in downtown Dubai, while Saudi Arabia said it had intercepted drones headed towards its Shaybah oil field and its embassy district.
With Gulf states slashing production and oil tankers stuck in the Gulf, benchmark oil prices have risen 40-50 percent since the US and Israel attacked Iran on February 28, threatening to crimp growth and stoke inflation.
"Oil prices are up by double-digit percentages again today, as the realisation sinks in that the US is not about to either end the war or institute some kind of convoy system in the region," said analyst Chris Beauchamp at IG trading and investment platform.
Energy Secretary Chris Wright acknowledged the US military was currently "not ready" to escort tankers through the Strait of Hormuz.
The war has upended daily life for Iranians.
A 30-year-old woman living in Kermanshah in eastern Iran said 90 percent of shops in her city had closed.
"People are desperately trying to withdraw their savings from the banks, as trust in them has vanished.
"Bread is now rationed. The population is extremely tense and outraged," she said.
The conflict has also spread to Lebanon, where authorities reported 687 people killed by Israeli attacks, including at least 12 who died in a strike Thursday on Beirut's blood-stained seafront where displaced families were camping in tents.
Israel's military said the Iran-backed Lebanese militant group Hezbollah had launched a barrage of 200 rockets and drones on Wednesday night in "a simultaneous attack with Iran" on Wednesday night.
Israeli Defence Minister Israel Katz said on Thursday he was ordering troops to "prepare for expanding" attacks on Lebanon.
Authorities in Israel said 14 people have been killed, while attacks in the Gulf have killed 24 people, including 11 civilians and seven US military personnel, according to local authorities and the US Central Command.
In Iran, over three million people have been displaced by the war, according to new figures issued Thursday by the UN's refugee agency.
Iran's health ministry said on March 8 that more than 1,200 people have been killed in the war, a figure AFP has not been able to independently verify.
