US President Donald Trump has issued a stern warning about the dire consequences that would result if Iran attacks the United States.

Israel and Iran traded fire for a third straight day on Sunday, with rising casualties and expanding targets marking a sharp escalation in the conflict between the longtime adversaries. Overnight Iranian strikes killed at least ten people in Israel,

The United States is the main international backer of Israel, Iran's biggest regional foe. It is also a close ally of Sunni Gulf monarchies which for years pursued their own rivalry with the Islamic Republic, seeing it as their main regional threat.

Trump told the Wall Street Journal that he knew all about Israel’s plan ahead of time, that he wasn’t given a mere “heads-up.”

President Donald Trump said early on Sunday that if Iran attacks the United States in any way, it would face the might of the US military “at levels never seen before.”

The United States has pulled some diplomatic staff and military families out of the Middle East, citing unspecified regional security risks.

Countries trade strikes as tensions grow over larger Middle East conflict - Iranian missiles struck an apartment building in the Galilee region, killing four people, as the countries exchanged fire

Iranian officials said on Friday that the United States "shall be held fully accountable" for its support of Israel after the nation took out key Iranian nuclear facilities and killed government leaders in a series of air strikes this week.