ERBIL, Kurdistan Region of Iraq - Israel on Saturday launched what it called a "preemptive strike" on Iran, with explosions being seen in Tehran and a nationwide red alert being imposed across Israel, with US media reporting soon after that Washington is also participating in the military operation.

"The State of Israel has launched a preemptive strike against Iran. Defense Minister Israel Katz has declared a special and immediate state of emergency throughout the country," read an Israeli defense ministry statement.

CNN, citing three US officials, reported that the US military is bombing Iranian targets, quoting one as saying it is "not a small strike."

Israel's Channel 12, citing a security official, reported that the ongoing strikes are part of a joint operation with the US.

"In the last few minutes, sirens were sounded all throughout Israel, with an advance instruction alert directly to cellular devices to stay within proximity to protected spaces," the Israeli military announced.

"This is a proactive alert to prepare the public for the possibility of missiles being launched toward the State of Israel."

Israeli Army Radio reported that official, missile, and security sites are being targeted in the operation.

Majid Akhavan, the spokesperson on Iran's Civil Aviation Organization, announced that the country's airspace has been closed until further notice.

Reuters said on Saturday morning, citing a security official, that Iranian Supreme Leader Ayatollah Ali Khamenei had been evacuated out of Tehran to a secure location. 

In addition to Tehran, explosions were heard in several Iranian provinces, including Isfahan, Qom, Karaj, and Kermanshah, Iranian semi-official media, according to semi-official Iranian media. 

US President Donald Trump told reporters on Friday, a day before the attacks, that they were not satisfied with the way Iran was negotiating, adding that Tehran is not willing to give Washington what it wants.

"I'm not happy with the fact that they're not willing to give us what we have to have. So I'm not thrilled," the US president said on Friday.

The attacks come amid renewed talks between the two adversaries, meanwhile, Trump had ordered the largest US military build-up in the Middle East since the Iraqi invasion in 2003, and has repeatedly threatened Iran that "bad things will happen" should the talks not yield any results.