Nine days after US-Israeli strikes killed Ayatollah Ali Khamenei and plunged the Middle East into war, Shiite clerics convened to choose the country's third supreme leader since the 1979 Islamic Revolution.

An announcer on state television solemnly read a statement from the 88-member Assembly of Experts next to a picture of the new 56-year-old leader, who bears a striking resemblance to his father.

Mojtaba Khamenei "is appointed and introduced as the third leader of the sacred system of the Islamic Republic of Iran, based on the decisive vote of the respected representatives of the Assembly of Experts", the statement said.

It said the clerical body "did not hesitate for a minute" in choosing a new leader despite "the brutal aggression of the criminal America and the evil Zionist regime".

State media soon afterwards showed a projectile said to be launched at Israel bearing the slogan, "At Your Command, Sayyid Mojtaba", using an Islamic honorific.

Explosions were also heard early Monday in Qatar, home to a major US air base.

The war came weeks after Iranian security forces crushed nationwide protests against the government, killing thousands. The younger Khamenei is considered a fellow hardliner who will pursue his father's rejection of dissent.

US President Donald Trump had previously dismissed the younger Khamenei as a "lightweight", and insisted again Sunday that he should have a say in appointing a new leader.

"If he doesn't get approval from us he's not going to last long," he told ABC News before the announcement was made.

Israel's military had also warned any successor that "we will not hesitate to target you".

- Oil price spikes -

As Iran retaliates against its oil-rich Gulf Arab neighbours, the benchmark price for a barrel of crude soared beyond $100 for the first time since Russia's invasion of Ukraine four years ago.

Trump dismissed the price spike, a politically sensitive issue in the United States, as a "small price to pay" for removing the alleged threat of Iran's nuclear program.

But markets in Japan and South Korea, both heavily dependent on energy imports, opened the week sharply lower on Monday.

In a sign that the United States does not expect a quick end to the war, the State Department ordered non-emergency staff to leave Saudi Arabia, days after a drone hit the US embassy.

Few expect major changes under the younger Khamenei, a trained cleric close to the Revolutionary Guards, the ideological arm of the military.

The Guards quickly pledged support for the new leader, who comes into the role with far less experience than his father, who had been president under the first supreme leader, Ayatollah Ruhollah Khomeini.

The Guards Corps said in a statement it was "ready for complete obedience and self-sacrifice in carrying out the divine commands" of the younger Khamenei.

Iran was founded on opposition to dynastic monarchies after the toppling of the pro-Western shah in 1979.

- Air 'unbreathable' -

Israel struck five oil facilities in and around Tehran early Sunday, killing at least four people and sparking blazes that left the skies filled with acrid smoke.

Tehran's governor told the IRNA news agency that fuel distribution had been "temporarily interrupted" in the capital.

A dark haze hung over the city of 10 million people, blocking out the sun, and the smell of burning fuel lingered in the air.

Authorities warned the fumes could be toxic and urged citizens to stay indoors, but many windows were blown out by the force of the blasts.

"The air has become unbreathable. I can't even go out to do the daily shopping," said one 35-year-old from Tehran.

"At first, I supported this war. After Khamenei's death, I celebrated with my friends: we drank wine and we danced.

"But since yesterday... people say there's not even any gasoline left at the gas stations," she said, in a text message to contacts in Europe.

Trump has sent mixed messages on the war aims. He has demanded "unconditional surrender" but also said that the war is all but won, and has also refused to rule out sending US ground troops.

The US military announced that a service member had died after being wounded in Saudi Arabia, the seventh American combat death in the war.

The Revolutionary Guards warned they had enough supplies to continue their drone and missile war over the Middle East for up to six months.

- War expands to central Beirut -

Israel struck a hotel in central Beirut on Sunday, the first attack in the heart of the Lebanese capital since the country was dragged into the war, with the Shiite movement Hezbollah vowing to avenge Khamenei's death with rocket attacks on Israel.

Israel said it had targeted five commanders of the Revolutionary Guards' international Qods Force, the patron of Hezbollah, as they met at a Beirut hotel.

Lebanon's health ministry said four people died and 10 others were injured in the Beirut strike.

In the east of the country, Hezbollah said its fighters were engaging Israeli forces who landed in 15 helicopters, one of which was hit by fire.

Lebanon's health minister said at least 394 people had been killed in Israeli air strikes since the start of the war, including 83 children and 42 women.

Saudi Arabia said Sunday that two people were killed and 12 wounded as a projectile landed in Al Kharj province.

Iran also fired new missiles at Israel, with several blasts heard over the commercial hub Tel Aviv, and the Magen David Adom emergency services saying six people were wounded in central Israel.

Several people were also injured in Bahrain, the interior ministry said, as Iran keeps targeting the small Gulf kingdom that serves as the base of the US Navy's Fifth Fleet.

Bahrain also reported damage to a water desalination plant, while Kuwait -- where the US embassy was earlier hit -- reported that an attack hit fuel tanks at its main airport.

Iran's health ministry said Sunday that at least 1,200 civilians had been killed and around 10,000 wounded -- figures AFP could not independently verify.

On Sunday, Pope Leo XIV prayed "that the roar of the bombs may cease, the weapons may fall silent, and a space for dialogue may open".

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