Supreme leader Ayatollah Ali Khamenei said Wednesday Iran will never surrender, with the country unleashing hypersonic missiles in a new wave of attacks against Israel on the sixth day of war between the longtime enemies.
The launch came hours after Israel said it had destroyed Iran's internal security headquarters in Tehran, and as it reported a new wave of attacks targeting missile systems and storage sites in the country's west.
Khamenei also warned the United States against becoming involved in the conflict, after President Donald Trump appeared to flirt with the idea in recent days, calling for Tehran's "unconditional surrender".
"This nation will never surrender," Khamenei said in a televised address, in which he called Trump's ultimatum "unacceptable."
"America should know that any military intervention will undoubtedly result in irreparable damage," he said.
Khamenei, in power since 1989 and the final arbiter of all matters of state in Iran, had earlier vowed the country would show "no mercy" toward Israel's leaders.
Iran's state television reported the launch of Fattah hypersonic missiles, while the Islamic Revolutionary Guards Corps also announced the launch of so-called super-heavy, long-range missiles.
An Israeli military official, who asked not to be named, said Wednesday that Iran had fired around 400 ballistic missiles and 1,000 drones since Friday.
About 20 missiles had struck civilian areas in Israel, the official added.
Israeli Defense Minister Israel Katz said earlier that air force jets had destroyed Iran's internal security headquarters, as AFP journalists in Tehran reported powerful explosions across the city.
He called the internal security facility "the main arm of repression of the Iranian dictator".
Meanwhile, a London-based internet watchdog said Iran was in the midst of a "near-total national internet blackout" on Wednesday after days of disruptions.
Iran later announced heavier internet restrictions due to "the aggressor's abuse of the country's communication network for military purposes", according to the Fars news agency. It first imposed internet curbs at the outset of Israel's campaign last week.
Trump has fueled speculation about U.S. intervention, saying Wednesday that his patience had "run out" with Iran, but that it was still not too late for talks.
He later said he has not yet made a decision on whether to join Israel in bombing Iran and warned that the country's current leadership could fall as a result of the war.
A change in Iran's government "could happen," he told reporters at the White House.
A day earlier Trump had boasted that the United States could assassinate Khamenei, but would not do so, "at least not for now".
United Nations chief Antonio Guterres warned against any "additional military interventions" in the Middle East, saying they could have "enormous consequences" for the region and beyond.
Israeli Prime Minister Benjamin Netanyahu, however, thanked Trump for his "support in defending Israel's skies" on Wednesday, calling him a "great friend" of Israel.
"We are striking the ayatollahs' regime with tremendous power," Netanyahu said in a televised statement.
"We are hitting their nuclear program, their missiles, their military headquarters, the symbols of their power," he added, acknowledging Israel had also suffered "painful losses".
Since Friday, at least 24 people have been killed in Israel and hundreds wounded, according to Netanyahu's office.
Iran said Sunday that Israeli strikes had killed at least 224 people, including military commanders, nuclear scientists and civilians. It has not issued an updated toll since then.
Israel said its surprise air campaign was aimed at preventing Iran from acquiring nuclear weapons -- an ambition Tehran denies.
Israel has maintained ambiguity regarding its own atomic activities, but the Stockholm International Peace Research Institute (SIPRI) says it has 90 nuclear warheads.
Beyond the deadly strikes, some Iranians have reported shortages in recent days.
Finding fuel has become a challenge, with long car queues waiting hours in front of petrol stations, a 40-year-old Iranian driver told AFP at the Iraqi border crossing of Bashmakh.
"There are shortages of rice, bread, sugar and tea," he said, asking to remain anonymous for fear of reprisals.
"People are shocked and distraught, they don't know what they should do," said a car dealer in the Iranian city of Bukan who also asked not to be identified by his real name.
Earlier, Israeli strikes destroyed two buildings making centrifuge components for Iran's nuclear program in Karaj, a satellite city of Tehran, the International Atomic Energy Agency said.
In another strike on a site in Tehran, "one building was hit where advanced centrifuge rotors were manufactured and tested", the agency added.
Centrifuges are vital for uranium enrichment, the sensitive process that can produce fuel for reactors or, in highly extended form, the core of a nuclear warhead.
French President Emmanuel Macron on Wednesday urged Israel to end strikes on targets in Iran not linked to nuclear activities or ballistic missiles, his office said.
Foreign governments have scrambled to evacuate their citizens from both countries since the conflict began.
But some Israelis stranded abroad chose to return home on special flights.
"I decided to come back because the family is here, and I belong here, and unfortunately we get used to these fights and war, but we prefer to be here, to support as much as we can," said Yaakov Bogen, a 66-year-old hotelier.