The US has launched “major combat operations” in Iran, designed to eliminate “imminent threats” from the country’s regime, Donald Trump announced on Saturday.

The operation is “massive and ongoing”, the US president said in a video on social media, pledging to use “overwhelming strength and devastating force” to destroy Iranian missiles and ensure it cannot develop a nuclear weapon.

A short time beforehand, Israel said it had launched “preventative” strikes on Iran, and was preparing for retaliation. Israel has closed its airspace.

Explosions were heard in Tehran, the Iranian capital, where smoke could be seen rising on the skyline, and several other cities. Iran has closed its airspace.

“The hour of your freedom is at hand,” Trump told Iranian citizens, urging them to “take over your government” once the operation is over.

Talks between the US and Iran on Tehran’s nuclear programme ended inconclusively on Friday, with a suggestion that further discussions would be held next week. Trump had said he was “not happy” with the progress of discussions.

Iran’s Supreme Leader Ayatollah Ali Khamenei is not in Tehran, and has been transferred to a secure location, an official told Reuters on Saturday.

Sirens were sounded in Israel to urge citizens to prepare the public for the possibility of missiles being launched in retaliation following its attack on Iran. naval presence