DUBAI, United Arab Emirates — U.S. President Donald Trump said Monday that the war against Iran may be short-lived despite the country’s selection of a new hard-line supreme leader to oversee the fight for the Islamic theocracy’s survival.

But moments later, Trump hinted during a news conference that the worst fighting could still be ahead as he threatened intensified action if Iran made any “attempt to stop the globe’s oil supply.” The back-and-forth sent oil prices and stock markets seesawing.

“We’re putting an end to all of this threat once and for all, and the result will be lower oil prices, oil and gas prices for American families,” Trump said.

The war has choked off major supplies of oil and gas to world markets and sent fuel prices rising across the U.S. The fighting has also led foreigners to flee from business hubs and prompted millions to seek shelter as bombs hit sites including military bases, government buildings, oil and water installations, hotels and at least one school.

The selection of hard-line Ayatollah Mojtaba Khamenei to succeed his late father as Iran’s supreme leader sent oil prices surging and markets sliding. Investors saw it as a signal that Iran was digging in 10 days into the war launched by the United States and Israel.

Oil prices later fell, and the U.S. stock market closed higher after Trump told a group of lawmakers at his golf club near Miami that the conflict may end soon.

“We took a little excursion” to the Middle East “to get rid of some evil. And, I think you’ll see it’s going to be a short-term excursion,” Trump said.

Trump also had a call Monday with Russian President Vladimir Putin to discuss the war and other issues. Putin’s foreign affairs adviser, Yuri Ushakov, said Putin “voiced a few ideas regarding a quick political and diplomatic settlement” of the conflict following his conversations with Gulf leaders and Iranian President Masoud Pezeshkian.

Khamenei, a secretive 56-year-old cleric, is only the third supreme leader in the history of the Islamic Republic. He has close ties to the paramilitary Revolutionary Guard, which has been firing missiles and drones at Israel and Gulf Arab states since his father, Ayatollah Ali Khamenei, who had ruled since 1989, was killed during the war’s opening salvo.

More than 20 heavy explosions were heard in Tehran in what was considered the heaviest air raid on the capital since the war started Feb. 28. Iranian media did not report on damages and casualties.

Israel said Monday that it was carrying out “a wide-scale wave of strikes” on the Iranian city of Isfahan, as well as Tehran and in southern Iran. The Israeli military said it hit dozens of infrastructure sites, including the drone headquarters of the Revolutionary Guard.

Meanwhile, Israel’s military said more missiles had been launched from Iran toward Israel late Monday.

Trump said the United States was nearing its goal to eliminate Iran’s ballistic missile stockpile and its ability to produce and launch them. The administration has offered shifting rationales and timelines since the start of the conflict.

He also talked about “building a new country,” a comment that seemed to suggest the U.S. might be engaged in the building of a new Iran.

Thousands poured into a central square in the capital, Tehran, and other locations in a show of allegiance to the new supreme leader, waving flags and shouting phrases like “Death to America” and “Death to Israel.”

The younger Khamenei, who has not been seen in public since the war started, was long considered a potential successor — even before the killing of his 86-year-old father.

Trump told reporters that he was “disappointed” that Mojtaba Khamenei was picked and that he liked “the idea” of a leader drawn from an “internal” group of candidates, saying that this process “works well” with Venezuela’s new leader, Delcy Rodríguez.

The younger Khamenei is seen as even less compromising than his late father. As supreme leader, he has the final say on all major policies, including Tehran’s disputed nuclear program.

Though Iran’s key nuclear sites are in tatters after the U.S. bombed them during the 12-day Israel-Iran war in June, it still has highly enriched uranium that’s a technical step away from weapons-grade levels. Khamenei could choose to do what his father never did — build a nuclear bomb.

Trump told reporters the war with Iran started because that country was starting work on a new site for developing material for nuclear weapons to replace one bombed last year by the U.S.

Israel has already described Khamenei as a potential target. Trump said Monday it “would be inappropriate” to say whether he would be targeted.

The U.S. stock market careened through a manic Monday, going from a steep early loss to a solid gain as worries turned into hope that the war with Iran may not last that long. Oil prices whipped from nearly $120 per barrel, the highest since 2022, back toward $90.

Iran’s attacks in the Strait of Hormuz have all but stopped tankers from using the shipping lane through which a fifth of the world’s oil is carried, and Iranian drones and missiles have targeted oil and gas infrastructure in major producers. Attacks on merchant ships near the strait have killed at least seven mariners, according to the International Maritime Organization.

Kamal Kharazi, foreign policy adviser to the office of the supreme leader, told CNN on Monday that Iran is prepared for a long war. He said he sees no “room for diplomacy anymore” unless economic pressure prompts other countries to intervene and stop the “aggression of Americans and Israelis against Iran.”

Turkey, meanwhile, said NATO defenses had intercepted a ballistic missile that entered the country’s airspace for the second time since the war started.

Saudi Arabia lashed out at Iran following the drone attack on its massive Shaybah oil field, saying Tehran would be the “biggest loser” if it continues to attack Arab states.

In the UAE, home to the futuristic city of Dubai, authorities said two people were wounded by shrapnel from the interception of Iranian missiles over the capital, Abu Dhabi. The Emirati Defense Ministry said 15 ballistic missiles and 18 drones were fired at the country on Monday.

Iran also attacked Kuwait, Qatar and Bahrain, where it hit a residential area, wounding 32 people, including several children, according to authorities. Another attack appeared to have started a fire at Bahrain's only oil refinery, sending up thick plumes of smoke.

The U.S. State Department early Monday ordered nonessential personnel and families of all staff to leave Saudi Arabia. Several other U.S. diplomatic missions have ordered all but key staff to leave.

The war has killed at least 1,230 people in Iran, at least 397 in Lebanon and 11 in Israel, according to officials.

A total of seven U.S. service members have been killed.

Trump said Monday that family members of the soldiers told him during the transfer of their remains over the weekend in Dover, Del.: “Make sure you win, sir.”