Explosions were heard in Tehran, state media reported, as the US and Israel said they launched strikes on Iran. Explosions have also been heard in Isfahan, Qom, Lorestan, Kermanshah, Karaj and Tabriz, Fars reported.
US President Donald Trump said that the US has begun "major combat operations" in Iran.
Shortly after, Israel said that "unidentified missiles" were launched from Iran.
"Defensive systems are operating to intercept the threat," the Israeli army said.
Mr Trump accused Iran of backing the October 7 attacks on Israel in 2023 and killing "thousands" of its own people.
The US is undertaking a massive and ongoing operation, he said. "We're going to destroy their missiles and raze their missile industry to the ground. It will be totally obliterated. We're going to annihilate their navy."
Mr Trump asked the Islamic Revolutionary Guard Corps (IRGC), the armed forces and police to "lay down their weapons and have complete immunity or face certain death". He called on the people of Iran to "stay sheltered" and not leave their homes.
"Don't leave your homes. Bombs will be dropping everywhere. When we're finished take over your government."
Israel's Prime Minister Benjamin Netanyahu confirmed that the strikes seek to topple the regime.
"Our joint action will create the conditions for the courageous Iranian people to take their destiny into their own hands," he said in a statement.
Iran's health ministry spokesman said hospitals are on alert and the number of casualties is yet to be determined, semi-official news agency Tasnim reported.
The operation was planned for months, and the launch date was decided weeks ago, the official added. The strikes are expected to be "more extensive" than during last year’s 12-day war, an Israeli source briefed on the operation told The National.
Potential targets in Iran include government facilities, military and intelligence targets. The source did not rule out Israel attacking high-ranking figures in the regime.
The source confirmed that the strike was a joint Israeli-US operation that was planned months in advance and said Israel is expecting several days of extensive retaliation.
Iran closed its airspace.
Iran’s supreme leader Ayatollah Ali Khamenei has been moved from Tehran to a secure location, an Iranian official told Reuters.
Mr Trump had recently been presented with military scenarios that included killing Mr Khamenei and his son Mojtaba, widely seen as a potential successor, according to US officials cited by Axios.
Mr Khamenei is Iran’s ultimate authority, with final control over the armed forces, nuclear policy and strategic decision-making. His survival is seen as essential to maintaining the command structure of both the state and the powerful Islamic Revolutionary Guard Corps (IRGC).
Israel's Mossad said it launched a "super secure and special" channel on social messaging application Telegram.
"Together we will return Iran to its glorious days", the Mossad's message said, referring to regime change in Iran following weeks of deadly protests.
Israel’s and US intelligence agencies have been increasing their attempts to engage with Iranians on the ground in recent days with the CIA posting a call on Tuesday for Iranians to share information with the agency.
Iranian lawmaker Ebrahim Azizi hinted that Iran would retaliate. "We warned you! Now you have started down a path which end is no longer in your control," he wrote on X.
The US embassy in Qatar said it is implementing a shelter-in-place order for all personnel and recommended that Americans in the country do the same.
Iraq has also closed its national airspace, the state news agency said.
Hours before the attack on Iran, Israel's army said it launched a wave of strikes on Hezbollah infrastructure across several areas in south Lebanon.
Such Israeli strikes on south Lebanon are not uncommon and Israel has killed dozens of people since a ceasefire announced between Israel and Hezbollah in November 2024.
