Israel has launched a daylight attack on Iran's capital, with a cloud of smoke seen rising from downtown Teheran near the office of Supreme Leader Ayatollah Ali Khamenei, who had been transferred to a secure location, according to media reports.

According to the Fars news agency, several missiles struck University Street and the Jomhouri area of the Iranian capital. Iran shut down its airspace soon after the attack began.

The United States is also participating in Saturday's strikes, according to a US official and a person familiar with the operation, who spoke on condition of anonymity, the Associated Press reported.

In addition, an Israeli defense official told Reuters that the latest Israeli attack against Iran was coordinated with the US.

Ahead of the attacks, the US had assembled a vast fleet of fighter jets and warships in the region in what was portrayed as an attempt to pressure Iran into a deal over its nuclear program.

"The State of Israel has launched a preemptive strike against Iran to remove threats to the State of Israel," Israeli Defense Minister Israel Katz said, as sirens sounded across Israel and the Israeli military warned civilians to stay close to bomb shelters.

While it wasn't immediately clear if Iran would immediately strike back, it had previously warned that US military personnel and bases which are spread across the region would be targets for any retaliation.

The US embassy in ?Qatar has implemented shelter-in-place for all ?personnel, recommending that all of ?its citizens do the same until further notice.