Donald Trump says Iran will be "hit very hard" and that the US and Israel plan to widen their scope of targets for "complete destruction".
His post on Truth Social came as Iranian President Masoud Pezeshkian rejected Mr Trump's demand for surrender as a "dream" and Tehran's hardline clerics were expected to meet within the next day to choose a new supreme leader.
"Today Iran will be hit very hard! Under serious consideration for complete destruction and certain death, because of Iran's bad behavior, are areas and groups of people that were not considered for targeting up until this moment in time," Mr Trump said in a post on Truth Social.
Mr Pezeshkian also apologised to Gulf states for missile and drone attacks — something Mr Trump cast as surrender — but later released a second statement denying Iran had attacked its neighbours, but "rather targeted American military bases, installations, and facilities in the region".
Hours after Mr Pezeshkian's announcement, Iran's Revolutionary Guards said their drones struck a US air combat centre at Al Dhafra Air Base, near Abu Dhabi, the capital of the United Arab Emirates.
The war has already spilled beyond Iran's borders, with Tehran responding by hitting Israel and Gulf Arab states hosting US military installations, and Israel launching fresh attacks in Lebanon after the Iran-aligned militia Hezbollah fired across the border.
Dubai was forced to briefly close its main airport — a key global transport hub — after an unidentified object was intercepted nearby. The UAE said it was targeted with 16 ballistic missiles and more than 120 drones on Saturday.
The Revolutionary Guards also targeted US forces at a base in Bahrain, Iranian state media said.
Blasts were also heard in Doha.
Speaking at an event hosting Latin American leaders in Miami, Florida, Mr Trump said the US had knocked out 42 Iranian navy ships in three days.
Israel launched what its military described as a new wave of strikes on Tehran and Isfahan, while overnight, the Israeli military said it had carried out strikes on neighbouring Lebanon that it said were aimed at Hezbollah military sites.
Israel has also issued fresh evacuation orders for parts of Lebanon, where authorities say the death toll has climbed to 294.
Iran's clerics set to choose new leader
Mr Trump had demanded a role in choosing a replacement for Iran's assassinated supreme leader Ali Khamenei, something senior figures in the Islamic republic have rejected.
Iranian media late on Saturday cited Ayatollah Hossein Mozafari, one of the 88-member Assembly of Experts, the clerical body charged with choosing the next leader, as saying the assembly could meet in the next 24 hours to make a decision.
It was not clear if that would involve an in-person gathering. Sources said some clerics had previously held consultations online.
Gulf states voiced outrage that their civilian infrastructure — hotels, ports and oil facilities — was struck despite them having had no part in the attacks.
The UAE, Kuwait, Qatar, Bahrain, Oman, Saudi Arabia and Iraq have all reported drone or missile attacks over the past week.
An Emirati official said the United Arab Emirates wanted the Iranian aggression against the Gulf states to end immediately.
"We don’t want the war to expand. We want to start with the Iranians realising that they are not helping themselves by attacking their whole neighbourhood and to stop there and realise that," the official said.
Israel strikes southern suburbs of Beirut
With the conflict spreading, Israel warned Lebanon of a "very heavy price" if it did not rein in Hezbollah, as it pounded the group's strongholds with air strikes and mounted a deadly airborne raid in the east.
On Saturday morning, more buildings in the southern suburbs of Beirut had been reduced to mounds of smoking rubble, dust and tangled wires, Reuters video showed.
Israeli Defence Minister Israel Katz, addressing Lebanon's President Joseph Aoun in a statement, said that if the Lebanese government failed to enforce a 2024 agreement to disarm Hezbollah, it and the whole country would suffer.
"If the choice is between protecting our civilians and our soldiers or protecting the state of Lebanon — we will choose the protection of our civilians and soldiers, and the Lebanese government and Lebanon will pay a very heavy price," he said.
The US-Israeli attacks have killed at least 1,332 Iranian civilians and wounded thousands, according to Iran's UN ambassador, Amir Saeid Iravani.
Iranian attacks have killed 10 people in Israel, and at least six US service members have been killed.
The Israeli military reported identifying missiles fired from Iran at Israel on eight different occasions on Saturday, setting off air raid sirens in parts of the country and prompting Israeli air defences to intercept incoming fire.
Mr Trump also reiterated his demand to have a say in selecting Iran's new supreme leader, a notion rejected by Mr Iravani.
The UN ambassador said new leadership would be selected "without any foreign interference".
