Donald Trump held a crisis meeting in the White House Situation Room as he prepares to make the biggest decision of his presidency - whether to engage U.S. forces in Israel's war with Iran.

The Situation Room gathering with top military and intelligence advisers lasted about 80 minutes and there was no immediate statement from the president.

Trump has already issued a chilling death threat to Iran's Supreme Leader, Ayatollah Ali Khamenei, revealing the U.S. knows his precise location and that he is an 'easy target.'

Four U.S. B-52 Stratofortress bombers are now stationed at the Diego Garcia base in the Indian Ocean, within striking distance of Iran.

The B-52s, which can carry nuclear weapons or other precision-guided bombs, were spotted on a runway at Diego Garcia on Monday.