Israel's military said it began targeting Iran-backed Hezbollah in Beirut's southern suburbs, after issuing an unprecedented evacuation warning for the entirety of the area that sent residents fleeing in panic.

The war has been felt as far as the Sri Lankan coast, where a US submarine torpedoed an Iranian warship, and Azerbaijan, which threatened retaliation after a drone hit an airport.

Trump on Thursday rejected the possibility of Khamenei's son, Mojtaba Khamenei, replacing his slain father as supreme leader, dismissing the younger man as a "lightweight".

"I have to be involved in the appointment, like with Delcy," Trump told Axios in an interview, drawing a comparison to Venezuela, where interim president Delcy Rodriguez has cooperated with him under threat of violence after the United States ousted her boss Nicolas Maduro in a military raid.

"Khamenei's son is unacceptable to me. We want someone that will bring harmony and peace to Iran," Trump told the publication, threatening more war in the future if a better alternative was not found.

The remarks suggest a willingness to work with someone from within the Islamic republic rather than toppling the government entirely, despite Trump's repeated exhortations for Iranians to rise up and take back their country.

- Beirut strikes -

Lebanon was dragged into the widening conflict on Monday, when Hezbollah attacked Israel to avenge the killing of Khamenei.

Israel responded with air strikes and sent ground troops into some Lebanese border villages.

In a message to residents of Beirut's southern Dahiyeh suburbs, an Israeli military spokesman said: "Save your lives and evacuate your residences immediately."

Israel's military later announced it had "begun striking Hezbollah infrastructure" in Dahiyeh.

The warning sent people fleeing from the area, with massive traffic jams on the outskirts of the suburbs, as people fired guns in the air, urging locals to leave as soon as possible.

On a Beirut beach, hundreds of families, many of them scared and angry, milled around after fleeing in haste, having nowhere else to go.

"We fled from the suburbs, we were humiliated," one man told AFP, declining to give his name.

"We'll sleep on the road tonight and God alone knows what will happen to us."

Lebanese authorities say at least 123 people have been killed, 683 wounded and at least 90,000 displaced since Monday.

- From Sri Lanka to Azerbaijan -

On Iran's borders, neighbour Azerbaijan warned a drone attack on an airport "will not go unanswered", raising fears of another country entering the war.

Iran denied being behind the strike and blamed Israel, but that did not stop Azerbaijani President Ilham Aliyev from accusing Tehran of "terrorism".

Australia, meanwhile, deployed two military aircraft to the theatre, and Canada's Prime Minister Mark Carney said he could not rule out his armed forces taking part.

Following fresh strikes on Iran's capital, AFPTV images showed blackened vehicles and mangled buildings, with smoke still rising from some.

"We're going through a very important page of our history and I'm not afraid," a 30-year-old Tehran resident told AFP. "Hope is the only thing that we have right now."

An Iranian state-run foundation said the death toll from US and Israeli strikes on the Islamic republic has risen to 1,230, a toll AFP could not independently verify.

The US military has reported the deaths of six of its personnel since the war began Saturday.

Iranian Foreign Minister Abbas Araghchi struck a defiant tone Thursday, saying Tehran had not sought a ceasefire and did not "see any reason why we should negotiate with the US".

Regarding the possibility of a ground invasion, he told US broadcaster NBC News: "We are confident that we can confront them and that would be a big disaster for them."

Israel, meanwhile, said 60 percent of Iran's missile launchers and 80 percent of its air defence systems had been destroyed.

Announcing a "next phase" in the campaign, army chief Zamir said Israel had "additional surprises ahead".

AFP reporters in Jerusalem heard explosions following warnings of incoming Iranian missile fire.

- Gulf under fire -

The conflict has not spared the rich Gulf monarchies, usually seen as a safe haven in a volatile region, as Iran has lashed out at cities and energy infrastructure.

Thirteen people, seven of them civilians, have been killed in countries around the Gulf since the war began, including an 11-year-old girl in Kuwait.

Qatar said Thursday it was intercepting an incoming missile attack as loud blasts, described by AFP journalists as the most intense yet, reverberated across Doha, where thick black smoke billowed across the horizon.

Falling debris from an intercepted drone also injured six people in Emirati capital Abu Dhabi, officials said.

In Bahrain, an Iranian missile strike sparked a blaze at the main state-owned oil refinery, which was later contained, the Gulf country's communications centre said.

And some Western diplomats in the Saudi capital Riyadh, meanwhile, said they were told Thursday to shelter in place, while a witness said the diplomatic quarter in the city had been closed off.

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