US President Donald Trump said Saturday that Iran's supreme leader Ayatollah Ali Khamenei was dead, after Israel and the United States launched an attack of unprecedented scale aimed at bringing down the Islamic republic.

Cheers could be heard on Tehran's streets after reports of the death of Khamenei, Iran's paramount leader since 1989, as plumes of black smoke hovered over the Pasteur district where he usually resides, witnesses told AFP.

"Khamenei, one of the most evil people in History, is dead," Trump said on his Truth Social network.

Israeli Prime Minister Benjamin Netanyahu earlier said there were "many signs that this tyrant is no longer alive".

Addressing the people of Iran, the arch-enemy of Israel and the United States since the 1979 Islamic revolution, Netanyahu said, "This is your time to join forces, to overthrow the regime and to secure your future."

The strikes prompted Tehran to fire off a missile barrage across the Middle East, with injuries and at least one death reported in explosions that rocked showcase cities in Gulf Arab monarchies.

Iranian authorities urged residents to evacuate the capital, a city of 10 million, while the country's Red Crescent society said that at least 201 people had been killed in the strikes and more than 700 wounded.

The Iranian judiciary said one strike that hit a school in the south killed 108 people, although AFP was unable to access the site to verify the toll or the circumstances surrounding the incident.

The UAE reported one civilian dead and damage from missiles in Dubai and Abu Dhabi, as blasts from Tehran's retaliatory salvo and air defences intercepting it also echoed over Israel, Saudi Arabia, Bahrain, Qatar, Jordan and Kuwait. 

Iranian Foreign Minister Abbas Araghchi had earlier told NBC News that Khamenei was alive "as far as I know", adding that "all high-ranking officials are alive". 

Also asked about Khamenei's health, foreign ministry spokesman Esmail Baqaei told the BBC he was "not in a situation to confirm anything", but "the whole system, the whole nation is focused on defending (our) national integrity".

In a sign that the fighting was far from over, Netanyahu said "thousands" of targets would be hit over the coming days, while Iran's top security official vowed a fierce reprisal.

The Israeli army said that Ali Shamkhani, an advisor to Khamenei, and the head of Iran's powerful Revolutionary Guards, General Mohammad Pakpour, were both killed.

Ali Larijani, head of Iran's Supreme National Security Council, said: "The brave soldiers and the great nation of Iran will teach an unforgettable lesson to the international oppressors."

'Barbaric'

Tehran residents had been going about their usual business when the strikes began. Security forces quickly flooded the streets, shops pulled down their shutters and few pedestrians risked venturing out, an AFP journalist saw. 

"I saw with my own eyes two Tomahawk missiles flying horizontally toward targets," a Tehran office worker told AFP before communications and internet access were cut. 

The Red Crescent said 24 of Iran's 31 provinces were affected by the strikes. 

Across Israel, city streets stood deserted as residents took cover in shelters while the blasts of intercepted Iranian missiles reverberated overhead. Emergency services reported two people injured.

Iran's Revolutionary Guards, meanwhile, radioed ships to say the Strait of Hormuz, a strategic waterway, was shut, according to the EU's naval mission and Iranian media.

'Eliminating imminent threats'

The attacks came after Trump expressed frustration at Iran's stance in negotiations over its nuclear and missile programmes.

In an earlier video address, Trump told Iranians the "hour of your freedom is at hand", urging them to rise up and "take over your government".

It was the first US military action of this scale apparently aimed at toppling a foreign government since the 2003 invasion of Iraq.

Israel's army chief Lieutenant General Eyal Zamir said the operation was "taking place at a completely different scale" than the 12-day war it fought against Iran in June, which the US briefly joined. 

A military statement called the operation "an extensive attack", saying it was the largest military air raid in the history of the Israeli Air Force".

Iran's Revolutionary Guards said their "missiles and drones have struck the headquarters of the US Navy's Fifth Fleet in Bahrain and other American bases in Qatar and the United Arab Emirates, as well as military and security centres in the heart of the occupied territories (Israel)".

Iran, Iraq, Kuwait, Syria, the UAE and Israel all closed their airspaces to civilian traffic, at least in part, and multiple airlines cancelled flights to the Middle East. 

Blasts across Gulf

Residents and AFP correspondents in the Emirati, Qatari and Bahraini capitals heard multiple rounds of explosions from Iran's retaliatory strikes.

In Qatar, people fled in panic as a falling missile plunged into a residential neighbourhood, erupting in a fireball as it hit the street.

And in Abu Dhabi, the UAE's capital, golfers were stunned to see dozens of projectiles flying overhead. 

In Bahrain's capital Manama, residents were hurriedly evacuated from the Juffair district housing the US Navy's Fifth Fleet. 

"When we heard the sounds, we cried out of fear," said Jana Hassan, a 15-year-old student who was in the area. "I will never forget the sound of those loud blasts." 

Two witnesses told AFP they heard an explosion and saw a plume of smoke rising from Dubai's famed man-made island The Palm, with authorities reporting four injured.

The foreign ministry of Oman, a mediator in recent US-Iran talks, called "on all parties to immediately cease military operations" and urged the UN Security Council to impose a ceasefire.