Four days after US and Israeli strikes killed Iran's supreme leader and triggered a regional war, AFP reporters in the Saudi capital saw smoke damage on the walls and roof of the embassy.

Saudi police were swarming over the diplomatic quarter and checking IDs of everyone who entered. Several roads were blocked, including approaches to the US embassy.

Powerful explosions also shook Tehran through the night, as fighter jets flew over the Iranian capital and US President Donald Trump threatened to escalate the conflict.

On Monday, the US State Department had urged "Americans to DEPART NOW" from all of the countries and territories of the Middle East "due to serious safety risks".

Israel, meanwhile, said it was seizing new forward positions inside southern Lebanon, after Hezbollah fired missiles in support of its backer Iran and provoked a furious Israeli bombardment.

Defence Minister Israel Katz said Israeli forces had been authorised "to advance and take control of additional strategic positions in Lebanon in order to prevent attacks on Israeli border communities".

- Burn any ship -

Following Israel's "escalation", according to a Lebanese military source, the Lebanese army redeployed troops in the south. Hezbollah claimed it had launched strikes targeting three Israeli bases.

In Gulf cities and the Omani port of Duqm, Iranian strikes continued to hit oil and gas infrastructure and as European markets opened the benchmark Brent crude price jumped again.

"We will burn any ship that tries to pass through the Strait of Hormuz," Revolutionary Guards General Sardar Jabbari declared, underlining the threat the war poses to the global economy.

In Washington, Trump warned that the strikes could continue for weeks or months.

"From the beginning we projected four to five weeks, but we have capability to go far longer than that," Trump said at the White House.

In an earlier interview with the New York Post, Trump -- who campaigned on promises to end US involvement in wars -- refused to rule out deploying US ground troops to Iran "if they were necessary".

And, speaking to NewsNation, Trump warned Iran would "find out soon" how he planned to retaliate for the Riyadh embassy attack.

The US president laid out for the first time the operation's objectives -- destroying Iran's missiles, navy and nuclear programme and stopping its support for armed groups across the region.

Trump's goals notably did not include toppling the Islamic republic, even though he and Israel's Prime Minister Benjamin Netanyahu have urged the people of Iran to rise up.

Saudi Arabia, home to one of the region's largest oil refineries, some which have already been closed following attacks, said it intercepted eight more drones in two cities, including the capital, on Tuesday.

Two, however, got through air defences and struck the US embassy, causing a fire.

In Fujairah, one of the United Arab Emirates, debris from downed drones caused a fire at an oil facility, the state's media office said. The blaze was brought under control and operations resumed.

- 'Imminent threat?' -

US Secretary of State Marco Rubio presented a strikingly new narrative of how the conflict started.

Washington's top diplomat said the United States, which had built up its forces in the Gulf to levels not seen since its 2003 Iraq invasion, attacked only after learning that ally Israel was to strike Iran.

Iran had been ready to strike US forces in the region in response to Israel, so Trump decided to intervene "pre-emptively" alongside Israel, Rubio said.

"The imminent threat was that we knew that if Iran was attacked -- and we believed they would be attacked -- that they would immediately come after us," Rubio told reporters before briefing lawmakers.

Rival Democrats voiced disbelief, with Senator Mark Warner saying it was "uncharted territory" for the United States to be triggered into action by Israel's perception of a threat.

Iran's foreign minister Seyed Abbas Araghchi responded that "there was never any so-called Iranian 'threat'."

"Mr. Rubio admitted what we all knew: US has entered a war of choice on behalf of Israel'," he posted on X.

In an earlier interview with the New York Post, Trump -- who campaigned on promises to end US involvement in wars -- refused to rule out deploying US ground troops to Iran "if they were necessary".

- Death toll rises -

Throughout the region, the death toll has steadily increased with six US military personnel killed so far in the war, according to US Central Command.

Iranian media have reported hundreds of Iranian casualties, including scores at a girl's school, although AFP reporters have not been able to verify tolls independently.

The US-based Human Rights Activists News Agency (HRANA) on Tuesday said there were 101 casualties inside Iran on the third day of the war, including "85 civilian deaths and 11 military personnel killed".

Many residents in Tehran were torn between fear of the bombings and hope that the government's days might now be numbered.

AFP journalists witnessed some residents with suitcases in hand preparing to leave.

"Every time we hear the noises, we get scared for just a second," a 45-year-old lawyer said in a voice message to Europe, "but we experience some joy and excitement every time we hear a hit."

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