The move, the first time the U.S. has attacked Iran, is a major escalation of the conflict between Israel and Iran.

President Trump calls attack "very successful", as Washington joins Israel's air campaign against Iran. Tehran had warned the US that any involvement would lead to retaliation.

Iran’s most heavily fortified nuclear site is at Fordo, a hilly area south of Tehran and about 15 miles away from Qum, a city where more than a million people live.