The war had sent stock markets slumping and oil prices soaring again on Monday as Tehran, under new leader Mojtaba Khamenei, fired a fresh barrage of missiles at its Gulf neighbors and signaled that the strategic Strait of Hormuz would likely remain closed.

But Wall Street then climbed into positive territory with Trump's repeated signals of a short-term conflict, despite the lack of details and amid threats that the United States could step up a war campaign that has hit more than 5,000 targets so far, according to the US military.

"It's going to be ended soon, and if it starts up again they'll be hit even harder," Trump told a news conference in Florida, after telling an audience of lawmakers that the campaign would be a "short-term excursion."

Trump's remarks came on the first day in power for the 56-year-old son of slain leader Ali Khamenei, with Iranian forces launching a fresh wave of missile and drone attacks on Saudi Arabia, Bahrain, Qatar, the UAE and Israel.

Another missile was also fired at NATO member Turkey -- the second such incident in five days -- with the alliance's air defenses intercepting it before it could reach its target.

With the Strait of Hormuz blocked to nearly all oil tankers, the price of benchmark crude oil contracts rocketed past $100 a barrel on Monday - their highest levels since Russia's invasion of Ukraine in 2022 - before pulling back.

French President Emmanuel Macron said his country and its allies were working on a "purely defensive" mission to reopen the strait, through which nearly 20 percent of the world's crude oil usually transits.

The mission would aim to escort ships "after the end of the hottest phase of the conflict," but experts say it would mean putting naval vessels at risk of fire from the nearby Iranian coast.

Kamal Kharazi, a foreign policy adviser to Iran's supreme leader, told CNN that Tehran was calculating that economic pressure would eventually prompt other countries to intervene and end the war.

Benchmark oil prices are up 40-50 percent since the US and Israel launched their attack on Iran on February 28, while stock markets worldwide are down, hitting pension funds and savings.

But those trends began to ease with oil prices dropping nearly eight percent at open of trade on Tuesday, though stock futures on Wall Street remained volatile amid Washington's mixed messaging.

- Rallies -

Iran faced a fresh blitz of US and Israeli strikes after its Assembly of Experts, the top clerical body, appointed its first new supreme leader in 37 years.

Iranian state media carried images of tens of thousands of people celebrating Mojtaba Khamenei's selection in central Tehran, many carrying his picture.

Iran's rebel Houthi allies in Yemen and the Hezbollah armed group in Lebanon pledged allegiance, while Russian President Vladimir Putin on Monday promised "unwavering support".

Trump told reporters he was "disappointed" about Khamenei's appointment, but remained open to a replacement from inside the Islamic republic, citing the recent transition of power in Venezuela as "a formula that has been very good so far."

Ali Ansari, a professor of Iranian history at the University of St Andrews in Scotland, told AFP the new supreme leader was a hardliner who had "been involved in all the most violent repressions that have taken place over the last 15-16 years".

Ali Vaez, of the International Crisis Group think tank, said the appointment was intended to send a defiant message that Trump's war "has only replaced one Khamenei with another".

- Oil risks -

Oil traders, policymakers and central bankers are all watching the Middle East for news about Gulf energy infrastructure, which is crucial for the world economy.

About 10 vessels in or near the Strait of Hormuz have come under attack since Iran blocked the waterway in retaliation for the US-Israeli strikes, shipping experts say.

Global shipping giant MSC announced it was formally halting some export shipments from the Gulf, meaning goods sitting on ships would be unloaded.

Following strikes on Bahrain's Al Ma'ameer oil facility that ignited a fire, the country's state-owned energy company Bapco joined its counterparts in Qatar and Kuwait in declaring "force majeure" -- a warning that events beyond its control may lead it to miss export targets.

The Saudi defence ministry said Monday it had thwarted a drone attack targeting an oil field in the kingdom's east, near the Emirati border.

- 'Resistance' -

In Bahrain, the interior ministry said early Tuesday an Iranian attack on a residential area in the capital Manama killed one person and injured others.

In Israel earlier, around 10 explosions were audible in Tel Aviv after the military announced it had detected missiles inbound from Iran.

At least one Israeli was killed when he was hit by shrapnel, emergency services said.

The multi-front war also intensified in Lebanon, where Israeli and Hezbollah exchanges of fire since March 2 have killed at least 486 people and wounded more than 1,300.

Lebanese President Joseph Aoun accused Hezbollah of working to "collapse" the state, while the head of the group's parliamentary bloc said it had "no other option... than the option of resistance."

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