The US president says "why wouldn’t there be a regime change?" after officials earlier said the strikes were aimed at ending Iran's nuclear programme.

President Donald Trump’s onslaught of Iran’s nuclear plants was the most violent moment of his two terms and America’s 46-year showdown with the Islamic Republic.

Iran condemned the U.S. attacks and asked the United Nations Security Council to “immediately act” to address “injustice and gross violations” by the U.S. and Israel. Iran’s Foreign Minister Abbas Araghchi said Israel with its surprise attack that sparked the war and the U.S. with its intervention this weekend each “ decided to blow up ” diplomacy.

The U.S. State Department on Sunday issued a "worldwide caution" alert for Americans traveling abroad, after President Donald Trump announced the U.S. had struck three nuclear sites in Iran.

The Department of Homeland Security issued an advisory June 22 warning Americans cyber attacks are likely, and violence in the homeland is possible.